We're taking a different approach. At the moment, we are designing the map layout on paper first in 2D. Then we will model the layout in 3D. Once we're happy with the design then we can start using Gtk Radiant for the actual map.
The problem is a lot of the ET maps are just badly designed and just look good visually. There is a reason why maps like Bremen, Special Delivery, Adler are popular. Their layout is well designed.
So if you're recreating a real location from Warsaw, make sure you don't just copy it. Change it up so that the layout would be better suited for ET