Thanks Josh,
The main thing the Op should realize is that a *very good* ad-hoc Vocal Booth can be made in a couple hours with materials from Walmart and Lowes (based on our posts) ... a sexy one at that.
While building a large VB with windows and room for instruments is an ambitious over-kill (IMHO), the end will probably only be *very good*. To be *excellent* (which our ears might not notice) probably requires a professional VB builder. The end result may be non-sexy, completely-vain, and a bulky nuisance ... wouldn't work for all types of vocal recordings (like multiple singers, instruments, etc.)
So the Op should only concentrate on his room echoes, outside sounds, a possible closet, fiberglass base-traps, and/or 'sexy' quilts. He really shouldn't make it ugly and chaotic.