Random Map Maker, Like in Transport Tycoon

Hello,

Im trying to find suggestions on how you would go about making a random terrain genrator like you see in Transport Tycoon, but only in 3D..

If someone could email or post some suggestions I would be greatful, so far I have gotten a random terrain to genrate using a excate height, but I can't seem to get it to genrate in a orderly manor, I was thinking that I might need to make a loop of some sorts to look for the terrain height next to the lowest terrain height.. ( Lowest Terrain Height is sea level.. then it goes up.. please get back to me

Thanks