I draw them with my hands and my very annoying laser mouse. (I miss my old ball-wheel mouse.)
Honestly, I have one of the top versions of Photoshop on my computer and I don't know how to use it, so I will tell you what I do...
I use MS Paint.
OK Stop laughing at me... it's true.
I import the picture I want to use into Paint and I start drawing on it with all the tools that MS Paint will allow. I copy and paste other sections of the building, if they are available, to fill in gaps and then draw the rest by hand.
It is very time consuming and often I am adding one pixel at at time to get the desired look. I have learned some pretty nifty tricks with Paint but it certainly has its limitations.
When I am fairly satisfied with the image in Paint I will then import it to Photoshop to do some final touches with the only few tools in PS I know how to use.... like blurring some lines or darkening an area or brightening it.
That's about it.
One day I'll learn how to use PS and do some real renders!