definitely the 10 x 20, less problems with bass! and standing waves even before treating the room.
what are a ceiling dimensions?...that is just as important
THanks on the 10 x20
I think I will have an option of 7 foot ceilings or vaulted to the roof shape. Is there a preference?
The vaulted ceiling will provide fewer parallel surfaces, which is desirable in an acoustically-minded room. Having 2 dimensions of the room as multiples of each other will be a little problematic but not as bad as when more than one dimension is the same (10x10, or worse yet 10x10x10).
But I'm not sure that a shed will be a good idea. Are you going to try for sound isolation from the outside world? What about ventilation? Climate control to protect your instruments and gear?
TBH, if you get the 10x20 room try to lose a foot off the 20. 10x19 will give you a lot better acoustic area than 10x20. Just saying.
That's what I was thinking too...sacrifice one foot on the length, and you've eliminated the common denominator. It may even be possible to utilize that extra foot for a storage closet or similar.
Would 1 foot deep book cases work?
Thats exactly what I was going to suggest, the books also act as a defuser to some degree.
Alan.