After you figure what sizes and multiples thereof, cut the board however possible. Make or buy a sanding block and buff the top of the board and the edges clean.
This next step is something that is little more than personal taste, but I like to lay the pieces out in order that way I am going know how much material I will have, and how thin I will have to stretch it in order to hit the target number of pieces.
Glue the pieces of the city fight terrain together using plastic model glue. USE GORILLA GLUE to glue the terrain pieces to the board that its based on. This is an expansive glue so you will need to weight the pieces down while its drying. Dry time is 1-2 hrs. If it is a large piece you will need another large piece of board to place on top. Use house canned goods to weigh it down.
Once the pieces are dry then it is on to flocking and I will let the video explain that!