help on how to make hills

A lot of people use insulation foam sheets to rough in the hills. These are big foam sheets from a building supply center that are used to insulate walls of houses. They are usually pink or blue. And then for best results cover the foam with plaster cloth. The plaster cloth is available at a craft store, or a hobby store. It's a mesh cloth with plaster in it. You just dip it in water and lay it over your base. Depending on the size of the diorama and the shape of the hills I sometimes use wadded up newspaper and then cover that with the plaster cloth. All you really need is something to support the plaster cloth until it dries. Another option might be chicken wire. Good luck with your diorama.

More info would be helpful as to size and type.

What I do is build up the general contours with styrofoam. either leftovers from purchases or the type you can get in the floral department of a craft store. Much smaller and easier to store than the insulation above. (But if you have storage and access, that would work, too.) I use Celluclay, a commercial papier mache for ground work. I mix this with an old style model railroad turn,. brown craft paint and white gule with just enough water to make a thick oatmeal thextured paste.