I need help with a model (again)

Sofar, I still model in truespace, but I usually only model with solid geometrical objects. This is fine for creating ships and bases, but makes modelling a landscape nearly impossible. I need object deformations for that, but I always mess up the model and PCS refuses to convert it.
Is anyone here willing to help me creating a landscape ? You don't need to texture it, just model and ensure it runs through PCS. Theoretically it should be no big deal for anyone with a little experience, I think I'm just to dumb to do so

I will provide a scetch of what I need, but the short form is this :
A giant object with some (small) mountains and craters on it. In the middle there should be a more or less flat place so I can place an installation there.
I would really appreciate any help in this matter

Thanks.