The size of the base would have to depend on the size of the tiles. With the 2D sketch we've been playing on, its 17 hexes at the largest on the y-axis, and 18 at the largest on the x-axis. We've been using 1" hexes, since the proxy models are smaller, but depending on the base size of the AR models that will probably have to be increased to 1.5 or 1.75". So, the base then would need to be around 30-33", pretty much in line with RRG's suggested size.
This will definitely be a 3D arena when its finally made. The raised platform area should be about 3-4" higher than the grassy lower area, the columns and statue will be real, any bushes or tress below, etc. Hopefully it will be able to store relatively flat, with the raised platform detaching from the board. That's why a modular design design is really attractive.
I haven't given much thought to the materials yet, largely because I've never done a project like this before. Those Battletech boards look amazing, and a lot of work. That might be the way to go though, and I'll definitely do some research on that, thanks.
Here's a small file of the playtest map we've been using
Some home rules we've been using
The columns and fountain are normal hazards
If you're pushed into the water, on your next activation turn you get a free attempt to get out. If you roll a 4+, you get out on the opposite side from where you were pushed. Otherwise, you get swept 5 hexes down the river and fatigue up. Each turn you get a free attempt for each of your models in the river. If you go over the edge (where the colour lightens), then you take 5 damage reduced by ARM.
You can move through the river so long as you have enough movement to get out the other side. On a 2+, you make it through, otherwise you are swept up and count as having been pushed in.
If you're pushed over the edge of the raised platform down to the grassy area, you take 5 damage reduced by armor. If you're pushed on to the lower step, you take 3 damage reduced by armor. No damage if you're pushed to the upper step.
From the upper platform, you can attack to the platform or upper step. From the upper step, you can attack the platform or the lower step. From the lower step, you can attack the upper step, lower step or the grass. From the grass, you can attack the lower step or the grass.
The 'wall' edge counts as spiked all along its length. The other three edges count as pits.
You can climb the platform's walls (hanging vines, etc) by 'spending' 3 movement, then rolling a 3+. If the roll fails, your movement ends.