Base builder zombie mod is an idea that totally warps the idea of a Half-Life zombie mod. If you're familiar with Counter-Strike Source zombie mods, then you are also aware of the physics which allows the user to essentially build his/her own barricade using couches and other objects laying around. Using this concept, I thought of moving this idea a step further and allow the user to create their own entire bases. After all, everyone likes to make their own maps. So why not let them?
Because every user is different and will like to build their own different styles of bases, every round is different. It is nearly impossible to recreate exact bases (unless the user has practiced significantly), so playing one map won't get too old too quickly.