Quote - "everytime i try to edit the infinite terrain, it shrinks"

That is odd. Anyway, the size of an infinite terrain can be edited, just like any other object. In fact, an infinite terrain is not infinite, it has 200Km x 200Km. If you want to view it from a high point and have low haze/fog, you'd probably want to make it larger.

See this thread for a discussion on this topic. My posts have some images about this.
http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3327802

Quote - "i would like to know how to make my own"

But you can. Just create a standard one and then edit the function that's behind the terrain generation. You can put whatever function you want there.