Hello, new fish here.

Started using sketchup recently, so far no problems, using it just for simple things.
However, i tried to match perspective to a photo of a building site i have here without much success. There is nothing else to match to except a slab of concrete of known dimensions that the building is going to be sitting on. Same slab of same dimensions is drawn into my model of the shed. Background is trees, no horizon (hilly place), but i know concrete to be level and certain of its dimensions.

Suggestions ?