Am I right to assume that if we build roads on top of it, the deposit of coal underneath will be gone?
Also, I know coal deposit is not gone underneath the building itself, but what about the doorway of the coal mine (the one marked with U?) Builders build road on the doorway so I think the coal deposit should be gone underneath it. Is that correct?

This information is very important especially for mission that has very minimal amount of coal like the last TPR mission.

For example
Land with coal deposit = x
Land = s
Coal mine =
888
8U8

Example coal field:

x x x x x x x
s x x x x x x
s s x x x x x
s s s x x x x

The optimal build will be like this:

x x x x x x x
8 8 8 x x x x
8 U 8 x x x x
s s s x x x x

Instead of somewhere in the middle.

Oh that's great to know, thank you!