One thing I will be careful with is to avoid having any mountains at the end of a runway LOL
I am sure many Terrain builders said, "OOOOOOOOPS."
Emh, no, the trees are what get them. You can see mountains from the tower. The terrain type under the base, and all that grass that might go with it, and the terrain type beyond the runways, and lastly, the mountains are what cause the problems.
Of the three, the mountains are the easiest to avoid, then the trees at the end of the runway. The Grass sticking out of the hanger floor and runways, that's what drive us nuts.
That's where you really need to know what you're doing.