Instantiate Random Level after a certrain distance the player move

First of all, thank you for trying to help me! Like in subway runner, etc. the order of the gameobjects are really random, and every certain distance there's a new random GameObject (PowerUp). let me clarify, my question is that I create endless runner right now, for exp. there's a blade "level" (with many rotating blades), a lazer "level", monster "level", etc. I call them "levels" but I want that after a certain amount of distance the player moves, (for exp. 500 meters) a new RANDOM "level" will instantiate. for exp. someone start the game and the first level he does is the blade level, but if someone else also starts the game, there's a chance it would be the monster level, and after a certain amount of meters he passes, the last level is "destroyed" and the new RANDOM level (except the level he just did) is instantiated. I hope you catched what I'm trying to say, and could help me :) I'd appreciate really much any help at all! Thanks a lot!