not sure what the specific issue is; this works perfectly fine, whcih is just the scripting of what you said you did;

note i'm using EXECUTE AS to directly test the permissions.

CREATE LOGIN [devtest] WITH PASSWORD=N'NotTheRealPassword' , DEFAULT_DATABASE=[master], CHECK_EXPIRATION=ON, CHECK_POLICY=ON

GO

EXEC master..sp_addsrvrolemember @loginame = N'devtest', @rolename = N'dbcreator'

GO

EXECUTE AS LOGIN='devtest'

select suser_name() ;--Am i DevTest? yes I Am

CREATE DATABASE myTEST;

REVERT; --change back into superman

DROP DATABASE myTEST;

DROP LOGIN devtest;