I think I'll join this and here is what I've come up with for terrain.

The gameplay will be quite different then most of the hero defenses, cuz here you won't be defending against creeps but against 10 waves of bosses coming 1 at a time.
Your temple has 3 lives and every boss that gets to it lowers it by 1 with the last boss taking 2. There will be several siege machines on the map that players can take control of like the catapult(the pillers building is where it stands).
I'm designing it for 4 players which I think is a decent number for a map like that.