Hi Karen,
I am half way thru building my obs. which is a faily flat roof with 2 seperate sections that will roll back onto the other half of the roof.
Some pics of my progress is
here.
I have a 50mm fall from top to bottom (looking at the last pics).
If you can put a partition in, you can have a warm area where you can setup an office type area and an area for the telescope. Probably need to go atleast 5x4m or 4x4m to have room. I have 6m diameter so putting a partition in across the middle. My openings are 2.4m^2.
Cheers