Here’s the board I created for my 10mm miniatures. It’s a 2’x3′ piece of plywood with a slightly smaller piece of sheet metal glued to that. I then coated the sheet metal in magnetic paint, mostly just to give it a little extra texture without losing any magnetism of the sheet metal. This all was then painted dark green and dry-brushed some lighter shades of green and yellow.
The hills were cut from standard foam core, which I then coated on top with more magnetic paint. Unfortunately this caused the hills to warp and become somewhat concave. I then glued sheet magnet to the bottoms of the hills and placed them under heavy weights to dry. This helped uncurl them, but they’re still not completely flat. I need to put some more thought on how to fix this problem. Finally, the hills were painted the same as the main board.
All my figures are mounted on #10 flat washers, which are smaller than an american penny, probably about 12 mm diameter. I placed a dab of Apoxie Sculpt into the hole of the washer, and then jammed the miniature down on it. This served both to fill the hole and to adhere the mini to the base. Once dry, I cut and stuck a piece of adhesive business card magnet to the bottom of each based miniature.
Thus, everything is magnetized to everything else — the hills to the board, the models to the board or hills. Even the castle has magnet stuck on its bottom, and by virtue of being made of tin allows the models to stick to it. The sheet magnet is probably the weakest of them, it works only well for light weight stuff with a large area, like the hills. The business card magnet is too weak for 28mm metal models, but works fine for plastics and these 10mm guys.
For 28mm guys I bought several years ago a huge pack of disk magnets that are easy to glue into the recess of your standard GW bases. Actually, I usually have to offset them with a small scrap of cereal box cardboard to get them level with the base of the miniature. Looks like now that site I linked has all kinds of cool shapes and sizes, and you could probably just base your mini right onto the magnet itself.
The magnetism is neat, and while it isn’t super strong (I wouldn’t want to turn the base upside-down), it does prevent anything from budging if you bump or tip the board. I also like using magnetism for transport. I buy a plastic toolbox to transport my minis in and coat all the bottom surfaces with magnetic paint. Then I can just place the minis in it where-ever I want, and they don’t bump into each other through normal transport.
Anyway, enough about magnetism, here are the pictures of my 10mm terrain: