Should i use terrain generation or make it myself for android?

I have a game concept that requires a set distance. For example Player needs to reach 300 meters.

From the terrain generators ive seen, none of them seem to match what i need. One of them had a background that scrolled with the camera and another had one type of generation as the level went on.

Basically what i need is control over what gets placed at what distance. So i would have normal generation but at 243 meters, i want there to be a big gap, then a big gap would generate (or whatever mesh i want) at 243 meters. I hope that makes sense.

Ive been thinking of making the terrain myself but i also dont want horrid frame rates especially for phone/tablet. So from what i remember there was a technique used for 3d games that let you unload previous areas to smooth out performance, would i be able to do that with this?

Its not an endless runner. It has a beginning and an end. Its just that end is very very far away depending on the level.