Will my roof construction allow attic flooring?
This is "Ridge board and rafters":



These are roof Trusses:



From your pictures, you clearly have ridge boards with rafters coming off of them.

The reason trusses shouldn't hold the weight of flooring or heavy boxes is because they are typically made from relatively small boards (2x4's in some cases) and the bottom board is already carrying a significant roof load because of the design of the angled elements.