CREATE FILE encountered operating system error 5 (Access is denied.) I'm trying to execute the following script in SQL Server Management Studio:
USE [master]
GO

CREATE DATABASE [test1] ON PRIMARY (
  NAME = N'test1', 
  FILENAME =
    N'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA\test1.mdf',
  SIZE = 70656KB , MAXSIZE = UNLIMITED, FILEGROWTH = 1024KB)
LOG ON (
  NAME = N'test1_log',
  FILENAME =
    N'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA\test1_log.ldf',
  SIZE = 164672KB , MAXSIZE = 2048GB , FILEGROWTH = 10%)

But I'm getting the error:

Msg 5123, Level 16, State 1, Line 2
CREATE FILE encountered operating system error 5 (Access is denied.)
while attempting to open or create the physical file
'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA\test1.mdf'.
Msg 1802, Level 16, State 4, Line 2
CREATE DATABASE failed. Some file names listed could not be created. Check related errors.

Already have all role permissions for my user, any ideas on what's wrong?
You are getting a permissions error.  The account which is running the SQL Server doesn't have the needed rights on the folder which will contain the database files.

You need to give the account which is running SQL Server (not your account) full control of C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA.