its a whole new issue with multilevel structures, they have to be leveled into the ground with crete and they cost alot more than the kill box open roofs, they also need to be structured to hold alot of weight and thats even more money.
thats why i say boat houses, they are multilevel and load bering. and alot of scrap yards will have atleast 1
also for those in charge of finding cheap wood and other parts; try asking shipping/ trucking companys if they have any crates they dont need . in cali we got like 100 for free and mand hallways and proper cover, you could also take them apart and salvage the woos for other parts, the ones we got were 7ft by 7ft. and held weight but still sketchy... no more than a light walk gets creaks