As per the video above, and my own limited experience, epoxy resin seems to be what you need. Before you begin, I would check out local stores and web sites that cater to the model railroad crowd for many of the materials mentioned in the video. I think your local Walmart will have modge podge. One web site I like is Micro-Mark, (
www.micromark.com). I think they sell quality stuff and may have about everything you need, including paints, brushes scenery supplies. Sign up for their home delivered catalog------you remember those things, lots of paper stapled together with words and pictures inside, they used to normally be found in man-cave toilets.
As far as raw materials for things like trees and bushes, use what nature has to give you. The roots of many plants turned upside down make the trunks of trees. Shake a little dried tree leaves on them and you have fall foliage. Copper stranded wire also makes a good tree. Twist the whole strand, or several strands together to make the trunk, then twist off several strands to make various branches. Keep on twisting fewer strands together as you make the branch longer until you get to the single strands. bend them at different angle to replicate the limbs of a tree. Paint it with a thick paint, to hide and blend the separate strands of wire so it's looks like bark, then paint them an appropriate tree color.
Use twigs to make your fence. The materials to make landscaping are as far away as your garden, park or woods.
I had a hibiscus plant die on me last winter and I've kept it to use to make some log cabins and the walls of a fort in a diorama I keep threatening to make.