You know how you got an idea in your head but just can't find a picture of it ? That's how i feel now. My idea is a trundle bed in where on bottom the mattress pulls out but the top mattress is omitted and simply is a hobby work area. http://www.walmart.com/search/search-ng.do?search_query=Trundles%20Bed&adid=22222222220207485247&wmlspartner=wmtlabs&wl0=b&wl1=g&wl2=c&wl3=31635183439&wl4=&veh=sem

I don't know what your ceiling is like or how handy you are, but you may wish to consider a pulley bed that you can winch up and down when guests are there.You can then use the space underneath for a large work area that can be laid flat on the floor underneath the bed when it is turned back into a guest room.A similar idea to this but with a proper winch system using chains to lock the bed in place...Failing that you need a foldaway bed in a cupboard...