There are many questions regarding how you have thought this through. The water must be removed, therefore it needs some form of gutter (for example, a hanging gutter). Where have you planned to place this?
Do you have enough slope for channel plastic? The joints usually don't become completely tight, and it usually requires at least a 1:10 slope for this.
It is not an optimal solution you have there, as has already been mentioned, rainwater must be able to be diverted. It also looks like there could be a pocket where potential snow can lie against the facade. Depending on the type of trees you have nearby, there may also be some debris in the form of leaves/needles that end up on the roof and retain moisture.
Even if you do everything "by the book," it's a risky construction with flat roofs and roofs that lean against a wall. Given the circumstances, a flat roof with a drain inside might probably work best anyway. Preferably welded tarpaulin, but tar paper might also work.
Unfortunately, you have plague, cholera, and the Spanish flu to choose from. It won't be really good no matter what you do.
