Well, you can't realy design a level with too-generic stuff, see:
http://www.gamedev.net/page/resources/_/creative/game-design/the-art-of-enemy-design-in-zelda-a-link-to-the-past-r4147
So, what i 'm thinking, first add some generic stuff to make it an actual MOBA:
- 2 players/teams
- 2 spawning-spots
- minion-waves
- towers
- XP-gain(or gold-gain, but then you'd have to add items as well, which might take a while)
edit:items can always be added later and just be traded against XP
then add variaty through (neutral) monsters
- cheap-reward monsters: close to the minion-lanes and not too strong
- expensive-reward monster: further to the edges of the map and a bit stronger
- special (temporary)boosts as rewards for specific monsters:
- damage against minions/towers
- better defense(damage-reduction and/or a slow to anyone who hits you)
- more XP-gain
- burn or poision damage onto your attacks
With these assets(or any you make up yourself) you should be able to play around and make a few different levels.
Don't forget you can play around with the lanes as well, and don't be afraid of having different stats on the different levels, LoL does this as well.
(like stronger(/weaker) minions, stronger boosts, or an overall faster XP-gain for fast levels.
Another thing to play around with is making minions stronger/different over time(maybe they get ranged attack or something)
but this is a bit more difficult to balance out, since minions also act as XP-sources(and they kill each other)
good luck.