Is it possible to go back in your level ?
I mean, is it like a randomly generated runner level where you go left to right in a never-ending way, or can your character go back on its steps like in a platformer ?
For a runner, you could consider something like having "structures" of the level in memory (in an array, or some text file for example) and create those on the fly when you are almost at the end of the current "scrolling".
A mix between the randomly generation from the endless runner template and something like
[quote:1e5qwtxk]Random Terrain generation via Midpoint Displacement - LINK
Procedurally create platforms - LINK
Generating terrain based on random templates - LINK
(Elements found in the How do I FAQ)