The landmark - reached in Week 13 of the project - means Phase One remains on course to be completed by the end of March.
The roof is only expected to be on for a short while as Town already have permission to build a second floor overlooking the pitch with more hospitality areas and rooms.
But it is needed so that the changing rooms and other ground floor facilities can be used while funding for the next phase is secured.
Chairman Ray Leader said: "I'm delighted that we are still on schedule given the scale of the project.
"It's exciting to come to the stadium and see the work progressing so quickly as we work to give this club and this town the facility it deserves."
Stadium manager Dave Stone has captured images of the new building as contractors ParryPage Projects have carried out the work.