FORM 4 [ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
                                                                                  
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OMB Number: 3235-0287
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      

1. Name and Address of Reporting Person *

GGC Opportunity Fund Management GP, Ltd.		 2. Issuer Name and Ticker or Trading Symbol

Cornerstone Building Brands, Inc. [ CNR ] 		5. Relationship of Reporting Person(s) to Issuer (Check all applicable)

_____ Director                    __X__ 10% Owner
_____ Officer (give title below)    _____ Other (specify below)
(Last)          (First)          (Middle)

C/O GOLDEN GATE PRIVATE EQUITY, INC., ONE EMBARCADERO CENTER, 39TH FLOOR		 3. Date of Earliest Transaction (MM/DD/YYYY)

2/3/2021
(Street)

SAN FRANCISCO, CA 94111
(City)        (State)        (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)

 
 6. Individual or Joint/Group Filing (Check Applicable Line)

___ Form filed by One Reporting Person
_ X _ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3) 		2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. Code
(Instr. 8) 		4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5) 		5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4) 		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V Amount (A) or (D) Price
Common Stock, $0.01 par value 2/3/2021  S  4233615 D$10.63 12441252.41 (5)(6)I See note (1)
Common Stock, $0.01 par value 2/3/2021  S  16385 D$10.63 48150.31 (5)(6)I See note (2)
Common Stock, $0.01 par value         2241786.43 (5)(6)I See notes (3)(4)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3)		2. Conversion or Exercise Price of Derivative Security3. Trans. Date3A. Deemed Execution Date, if any4. Trans. Code
(Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date7. Title and Amount of Securities Underlying Derivative Security
(Instr. 3 and 4)		8. Price of Derivative Security
(Instr. 5)		9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)11. Nature of Indirect Beneficial Ownership (Instr. 4)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
Explanation of Responses:
(1) Shares are directly held by Atrium Intermediate Holdings, LLC ("Atrium Intermediate"). Atrium Window Holdings, LLC ("Atrium Holdings") and Atrium Window Parent, LLC ("Atrium Parent") are the members of Atrium Intermediate. Atrium Parent is the controlling unitholder of Atrium Holdings. GGC Atrium Window Holdings, LLC ("GGC Atrium') is the controlling unitholder of Atrium Parent. GGC BP Holdings, LLC ("GGC BP") is the controlling unitholder of GGC Atrium. The Funds collectively hold all of the equity interests of GGC BP. Each of Funds, GGCOF Third Party Co-Invest, Management GP and Ultimate GP disclaim beneficial ownership of these shares except to the extent of their respective pecuniary interests therein.
(2) Shares are directly held by GGC BP. Each of the Funds, GGCOF Third Party Co-Invest, Management GP and Ultimate GP disclaim beneficial ownership of these shares except to the extent of their respective pecuniary interests therein.
(3) Shares are directly held by AIC Finance Partnership, L.P. ("AIC"). Each of Golden Gate Capital Opportunity Fund, L.P. ("GGCOF"), Golden Gate Capital Opportunity Fund-A, L.P. ("GGCOF-A"), GGCOF Co-Invest, L.P. ("GGCOF Co-Invest"), GGCOF Co-Invest IRA, L.P. ("IRA Co-Invest") and GGCOF Executive Co-Invest, L.P. ("Executive Co-Invest" and, together with GGCOF, GGCOF-A, GGCOF Co-Invest and IRA Co-Invest, the "Funds") have an indirect pecuniary interest in AIC. GGCOF Co-Invest Management, L.P. ("GGCOF Third Party Co-Invest") is the general partner of each of GGCOF Co-Invest, IRA Co-Invest and Executive Co-Invest. GGC Opportunity Fund Management, L.P. ("Management GP") is the general partner of each of GGCOF, GGCOF-A and GGCOF Third Party Co-Invest, and GGC Opportunity Fund Management GP, Ltd.
(4) (Continued from Footnote 3) ("Ultimate GP") is the general partner of Management GP. Ultimate GP is governed by its board of directors. Each of the Funds, GGCOF Third Party Co-Invest, Management GP and Ultimate GP disclaim beneficial ownership of these shares except to the extent of their respective pecuniary interests therein.
(5) On July 17, 2018, Cornerstone Building Brands, Inc. (formerly known as NCI Building Systems, Inc.) (the "Issuer") entered into an Agreement and Plan of Merger (the "Merger Agreement") with Ply Gem Parent, LLC a Delaware limited liability company ("Ply Gem"), and for certain limited purposes set forth in the Merger Agreement, Clayton, Dubilier & Rice, LLC, a Delaware limited liability company. Pursuant to the terms of the Merger Agreement, at the closing of the merger, Ply Gem was merged with and into the Issuer with the Issuer continuing its existence as a corporation organized under the laws of the State of Delaware (the "Merger").
(6) (Continued from Footnote 5) As consideration to the holders ("Holders") of Ply Gem's LLC interests (the "LLC Interests") as of immediately prior to the closing of the Merger, at the closing of the Merger, the LLC Interests were converted into the right of the Holders to receive, in the aggregate with respect to all such interests, 58,709,067 shares of Common Stock (collectively, the "Aggregate Merger Consideration"), with each Holder being entitled to receive its pro rata share of the Aggregate Merger Consideration (the "Stock Issuance"). Each of Atrium Intermediate and GGC BP were Holders prior to the Merger. Pursuant to the terms of the Merger Agreement, following a Special Meeting of the Issuer's shareholders held on November 15, 2018, the Issuer's shareholders approved (i) the Merger Agreement and (ii) and the Stock Issuance. The Merger was consummated on November 16, 2018.

Remarks:
Exhibit 24 - Power of Attorney (incorporated by reference to Exhibit 24 to the Form 3 filed by the Reporting Persons on November 23, 2018).

Form 1 of 2
Reporting Owners
Reporting Owner Name / Address
Relationships
Director10% OwnerOfficerOther
GGC Opportunity Fund Management GP, Ltd.
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

ATRIUM INTERMEDIATE HOLDINGS, LLC
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

ATRIUM WINDOW HOLDINGS, LLC
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

ATRIUM WINDOW PARENT, LLC
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

GGC ATRIUM WINDOW HOLDINGS, LLC
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

GGC BP HOLDINGS, LLC
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

GOLDEN GATE CAPITAL OPPORTUNITY FUND, L.P.
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

GOLDEN GATE CAPITAL OPPORTUNITY FUND-A, L.P.
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

GGCOF Co-Invest Management, L.P.
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X

GGCOF CO-INVEST, L.P.
C/O GOLDEN GATE PRIVATE EQUITY, INC.
ONE EMBARCADERO CENTER, 39TH FLOOR
SAN FRANCISCO, CA 94111
X
Signatures
GGC Opportunity Fund Management GP, Ltd., By: /s/ Stephen D. Oetgen, attorney-in-fact for David Dominik, a Director2/5/2021
**Signature of Reporting PersonDate

Golden Gate Capital Opportunity Fund, L.P., By: /s/ Stephen D. Oetgen, attorney-in-fact for David Dominik, a Director2/5/2021
**Signature of Reporting PersonDate

Golden Gate Capital Opportunity Fund-A, L.P., By: /s/ Stephen D. Oetgen, attorney-in-fact for David Dominik, a Director2/5/2021
**Signature of Reporting PersonDate

GGCOF Co-Invest Management, L.P., By: /s/ Stephen D. Oetgen, attorney-in-fact for David Dominik, a Director2/5/2021
**Signature of Reporting PersonDate

GGCOF Co-Invest, L.P., By: /s/ Stephen D. Oetgen, attorney-in-fact for David Dominik, a Director2/5/2021
**Signature of Reporting PersonDate

Atrium Intermediate Holdings, LLC, By: /s/ Stephen D. Oetgen, attorney-in-fact for David Thomas, a Manager2/5/2021
**Signature of Reporting PersonDate

Atrium Window Holdings, LLC, By: /s/ Stephen D. Oetgen, attorney-in-fact for David Thomas, a Manager2/5/2021
**Signature of Reporting PersonDate

Atrium Window Parent, LLC, By: /s/ Stephen D. Oetgen, attorney-in-fact for David Thomas, a Manager2/5/2021
**Signature of Reporting PersonDate

GGC Atrium Window Holdings, LLC, By: /s/ Stephen D. Oetgen, attorney-in-fact for David Thomas, a Manager2/5/2021
**Signature of Reporting PersonDate

GGC BP Holdings, LLC, By: /s/ Stephen D. Oetgen, attorney-in-fact for David Thomas, a Manager2/5/2021
**Signature of Reporting PersonDate
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