A very interesting idea..but If it's a real formerly used one, then I won't volunteer to help clean the you know what before the remodeling!
Where and what configuration you use for nests and roost depends on the size of the outhouse. You could consider opening to outside to collect eggs and use the two seat area for nests, have seen a new build that did that. Make sure the roosts are higher than the nests with easy chicken access and arrange so their poop at nite doesn't fall into the nests.
Search google for chicken coop outhouses and bet you can find some examples.
Would love to see what you come up with.
