Hey Chris welcome to the Observatory Forum where almost anything is possible! We need some pictures of your roof top site, some info on your telescope and the size of the observatory you want as well as the size of the lift in the building. Just how solid is that solid wall? How old is building and whats the roof made of? Do you live on the 13th story? If not who's flat is under where you want to build? Will they mind hearing you mucking about while you build, while you observe or roll the roof back and forth?