How is this done properly

What kind of roofing is on it now?

A little more information about the surface, like is it flat or pitched, even slightly pitched.

Any drains/gutters?

KBC

I have an old cornshed , rectangler in structure about 10'x6'x10'tall, with no roof roof was removed from being damaged. Looking to put in a new roof at 45 degree angle I saw what looked like metal post on the corners.