Observational drawing- Rooves

I dont like this piece of work. I think that it looks flat due to the fact that i have used to much black chalk on it. i think to improve this i would have to focus more on shadow and could possibly add a colour in to add some depth. I also think that to do a better observation of this scene i would have to have something with a finer end to add in the bits of detail which i feel are missing.