So Im in the process of making my first map, and I want to make much more than a basic map. My idea is to have the player standing atop a tower defending from zombies on all sides possibly with only snipers.

The only problems so far are two things:
-Since I cant have the zombies climb up the tower to kill the player, is there a way to have the game end if the zombies reach the center (much like Ping998's map ALIEN DEFENSE in which the game ends if the zombies walk on a teleporter pad)
-If I decide to go the snipers only route, which I may not either way would be fine, how would I make a mystery box that only gives the player snipers

Both of these will be solved via scripts. The guns that are available in the box are determined in one of the gsc files. To end the game when a zombie reaches an area would require a trigger_radius in radiant and an accompanying script to check for enemy ai in the radius.