Ok.. I have an 18x18 looking for Ideas... I like to be simple Storage and crafting areas.. Not alot of clutter.. Clean Simple Design.. Any ideads appreciated.. I don't mind if ur pics have deco in it.. Just need the House layout ideas.. 
Post some pics... Sounds very interesting...You could also set up a "basement" where you do your work (two stairs along the south wall for access to the second "first" floor) That way you have a large area to do a lot of work with (18x17) and you can keep it very private, even if your house is open to the public. I've been designing my guildhouse on Siege for the last week or so and that's the style that I'm going for so far, the second/third floor are the guild hall though (similar design to a auction house).
I found some great design ideas while going through the Post Your Custom House Designs Here thread. Tying a lot of them together to make something very large and impressive. To be honest though, I am not even in a Guild... not sure why I want to build a guild hall. (shrugs)
You could also set up a "basement" where you do your work