Do you already have the mountain built? If so, pick a gradient that you want......I never go over 2.0% and start laying the track. You'll have to make it weave all around (back and forth) until you find the next place for it to touch the ground. If you do not have the mountain built, again pick you desired grade and start laying track. Then go back and fill in the mountain under the track. (I prefer this way, but your mileage may vary.)