GRANT CREATE TABLE TO [User1]
GRANT ALTER ON SCHEMA::MySchema TO [User1]

USE master
GO
DROP DATABASE TestDB

CREATE DATABASE TestDB
GO
USE TestDB
GO

CREATE SCHEMA TestSchema AUTHORIZATION dbo
GO
CREATE USER [User1] WITHOUT LOGIN
GO

-- Fails - CREATE TABLE permission denied in database 'TestDB'.
EXECUTE AS USER = 'User1'
CREATE TABLE TestSchema.UserTable (i int IDENTITY)
GO

REVERT 
GO

GRANT CREATE TABLE TO User1

-- Fails - The specified schema name "TestSchema" either does not exist or you do not have permission to use it.
EXECUTE AS USER = 'User1'
CREATE TABLE TestSchema.UserTable (i int IDENTITY)
GO

REVERT 
GO


GRANT ALTER ON SCHEMA::TestSchema TO USER1

-- Works!
EXECUTE AS USER = 'User1'
CREATE TABLE TestSchema.UserTable (i int IDENTITY)
GO

REVERT 
GO

-- DBO adds a new row
SELECT * FROM TestSchema.UserTable
INSERT INTO TestSchema.UserTable DEFAULT VALUES
SELECT * FROM TestSchema.UserTable


-- Fails - The SELECT permission was denied on the object 'User1', database 'TestDB', schema 'TestSchema'.
EXECUTE AS USER = 'User1'
SELECT * FROM TestSchema.UserTable
GO

REVERT 
GO

USE master
GO
--DROP DATABASE TestDB