I built this up for one of my kids, and again have not got the time to produce a full instructable (as yet).
The base is 10mm chipboard. The "case" is clear acrylic sheet, with the joints being made with off the shelf 90 degree wood profiles. The side panels are cut from hardboard.
The basic contours and elevations are built up with corrugated cardboard, from old boxes. Newspaper or paper towels soaked in PVA glue and water (wood glue or kids glue, the white water based stuff that dries clear) are laid on top (plaster of Paris, or proprietary casting plaster can be used) .
The cliffs are polystyrene packaging, I used cellulose thinners on a cheap artists paintbrush (many solvents may work, petrol etc) to carefully melt the face to create a “rock” like finish. Be careful if you try this, for one thing, cellulose thinners are toxic and highly flammable, for another I don't know what if any, fumes are liberated when the polystyrene is melted in this way.
(USA Cellulose thinners,- Lacquer thinners? Polystyrene, - Styrene? Chipboard, - Particle Board?)
The “building” again is just polystyrene packaging material, with a few bits nipped out.
The “river” is a combination of acrylic varnish poured in layers to about 10mm, topped with a proprietary model makers “model water”. This stuff is warmed up and poured, it then sets to a solid rubber like finish. I tried to add some further realism with blue and white kids water based paints. A Grunt can be seen dispatched in the water.
The figures and model Warthog, are all from the Halo Action Clix series, with their bases removed and extra paint in places. These are available cheaply, I actually ordered most from the US via ebay. I was limited as I did not want to order the rarer expensive figures, so you can see the battle would not be strictly “historical”. Basically marines killing anything alien is the game plan. They can be warmed with a heat gun to bend or reshape, for example the dead Elite. The stock blue character, has been removed from the turret gun and replaced with the easily available Mastercheif figure.
Grass areas are firstly painted green, mud areas brown, then PVA glue is painted on, followed by coloured flock sprinkled over the top (or sawdust you dye with kids paint). The cliffs are painted with kids water based greys and whites, and also black enamel paint is detailed in while the water based paint is still wet. Some cement powder adds dust for the damaged areas. The attempts at bushes are fashioned from the stuff available from model shops.
To show some detail, click on the images then select "LARGE(1024x768)" from the left hand menu. Or click "Original File" at the bottom of the picture, you can then zoom in.