Sandbox Mode

I'm pretty sure someone has come up with this before, but I was not around to see it. I think a sandbox mode would be fantastic for trying out new items and whatnot. You would have unlimited gold access, the option to turn minions waves on or off, and the ability to place minions, monsters, or even AI champions anywhere on the map. You could customize the items and stats on the champions, even going as far as selecting one of your rune/mastery pages to be put on them. Maybe even have the option to make them stand still and do nothing. This would be phenomenal for testing out builds and seeing how they work against other builds/champions. I love trying new things. I'm constantly changing up builds or testing out new ideas to see what works or what could improve my game. There's always the option of making a custom, but it takes 30+ minutes to get all the items you want. Not only that, but being able to place minions/monsters/champions anywhere on the map to test item/ability ranges or even item combos would help tremendously. I don't see much downside to this besides the ability to find and exploit bugs, but it would be a great addition to League of Legends in my opinion. What do you guys think?