I make all Yama survival maps : Tokyo, Ropeway and Hotel
In Tokyo Survival, it is too easy to have the gold, you can stay inside the truck and wait the bots kill zombies. Strangely, Specials never come and Tanks too, even if they spawn, they disappear after few second.
If you want more challenge, make a survival in Ropeway or Hotel.
I think it is interesting to make a Survival Versus in Hotel Survival