considering how soon Christmas is I don't think it's going to be done before that. So, if I were in your boyfriend's shoes, I'd love on Christmas day to open up a package that has all sorts of garage type materials, info, pictures, catalogues etc. Include maybe a handmade coupon that entitles him to "a space of his own" or something. Maybe you include a $$ amount that he could spend or a gift card to get him started... I dunno. Guys have certain things in mind (despite what our better halves think) and maybe what he'd love is something you wouldn't think is important. I'd hate you to spend money on something he didn't necessarily think was important.
I'd somehow try to include him in your present and make it a project to work on together. Aside from that, I'd think as mentioned earlier drywall, paint and some new light fixtures would make that space look really good.
Good luck and welcome to the board!
Piper