Wills kits are made from moulded polystyrene plastic and their Scenic Series kits can be built quite easily with a sharp craft knife, file or abrasive paper and a suitable solvent adhesive (either plastic cement (from a tube) or liquid solvent from a bottle). Then they just require painting to enhance the look, although they are made in a colour of plastic closely matching the material being represented.
There are over 50 kits in the range Scenic Series range, as well as bridge systems, materials packs (wood planking, cobble stones, tiles, etc.) and building accessories (doors, windows) for the scratch builder.
All of these items are in the 'OO' scale of 4mm/ft.