>>6811770I make wargaming terrain, it's pretty easy depending on how intense you are about it. There's the old pink insulation foam mountains which are quick and easy with a hot foam cutter.
Alternatively you can do cork mountains for about as cheap but it takes a bit more work to look good.
For more woodland stuff like trees you can do the quick twist brush tress (get two pieces of metal I use Bailing Wire, get a cheap broom head or brush from the dollarstore or wherever, put the two pieces of wire in a drill and put the brush bits in between and slowly wind it.) Takes a bit to get the hang of but they look decent, add some white glue, flock, and paint and they're done. Alternatively you can make complete wire trees and putty them up but that takes ages and is more expensive.
On top of that you want Gesso paint for priming since it will seal and protect everything. It also turns cork into stone so it's handy for solidifying stuff.
You'll want flock which is like stuff for dirt and rocks. You can make your own with fine sawdust or sand with bits of cork and stuff in it (to emulate small stones and what not).
I usually build my stuff on 1x1 foot squares so they're easy to store and you can mix and match pieces for different layouts.
Just make sure you have a solid base like MDF or something. Plywood can be alright but it's also more prone to warping so make sure you properly seal all your pieces.
anyway, feel free to ask me anything or hit up /tg/ as there's people there who do this everyday, there's no dedicated thread for terrain though usually so ask around.