Is somebody interested in detailed tutorial?
I made e.g. Big Ben in London, can describe how to do it.
Praha has a lot of beautiful landmarks but eone need a lot of time to get good results. Please try it with simliest buildings in one area.
I think for a lot of historic roofs in Praha you need to work with roof:edge and roof:ridge.
Btw: Nice example from Poland: http://demo.f4map.com/#lat=51.0416419&lon=21.0867565&zoom=20&camera.theta=59.66&camera.phi=-51.28