"Unlimited" game customization?

I feel like there should be unlimited resources when customizing a match. This would allow the player to save tons of time when simply trying new builds and making item purchases. The current custom game play options seem to limit the player to learning champion and item basics. If we would be allowed to create custom matches in which we can complete item builds before the match even starts (due to unlimited gold income or every item is free of purchase), we could play a match for mere minutes and figure out if certain items are worth incorporating into a build or if they hinder the overall play-style.