Building your own terrain is a lot of fun and in my opinion a major part of the gaming hobby. In Necromunda terrain is even more important than in other wargames. Necromunda is a Hive world and the games are supposed to take place in the lower levels of one of those Hives. So you need a lot of terrain (especially buildings) to fill up your gaming table. The basic boxed game comes with several cardboard buildings, but in my opinion still not enough. So unless you buy your terrain for a lot of money (wich I prefer to spend on the minis) you have to build your own.