Well...just keep in mind that if you do the typical walls/ceiling build...you may need more work inside to make it sound good.
It really comes down to what "good" means to you....and if this is more of a man cave thing, then you won't need to go nuts compared to say...if you wanted this to be a "good" sounding recording studio space..etc.
I say this because you're still at the early stage with the walls/ceiling...so think about all that, because you have the opportunity to build the "good" into it more so now, than you will later.