So it would be just a regular 5v5 game.
The only difference is that you would be only allowed to buy 1 item the entire game. So you would really have to rely on your runes, masteries, item choice, and champion choice to win the game.
Potential Variations
1. Classic
Only 1 item is to be bought for the duration of the game.
2. Kill Game Variation
You are allowed 1 item at the start of the game. For every kill you get (not assists) you can use an additional item slot. So if you have no kills you're stuck at 1 item. If you have 4 kills you can get 5 items.
3. LVL 18 Variation
You are allowed 1 item at the start of the game. Upon reaching LVL 18, you are allowed to use all of your item slots.
4. Ulti Variation
You are allowed 1 item at the start of the game. For every level on your ultimate ability, you are allowed to use another item slot.
5. Farming Variation
You are allowed 1 item at the start of the game. For every 100 cs you have you are allowed to use another item slot. For example, at 100 cs (farm) you can use 2 item slots. At 234 cs, you can use 3.
Just an idea right now, thoughts?