Sorry, I didn`t see your post until today.
The size of the kidneys depends on your gaming table and on the style you want to achieve. My goal was to have some hills which are fully walkable for the mechs. But I also have some w.i.p. hills for my dessert (with a different technique) which can only be mounted by jumping mechs.
The good thing with hills or rocks is, that you do not really have to care about scale or shape (from the aesthetic perspective). Just try out what is pleasing for you.
For making these hills I used a lot of scrap foam pieces. Unfortunately I can`t give you the rectangular measurements but I can give you some dimensions of the finished products. These are the biggest:
And these are the smallest ones:
Do not make them smaller if you want your mechs to have a solid stand on them.
By cutting and carving the rocks you will loose maybe round about 2cm (0,79inch) on each side. But you can always take away more if you want or need to. So maybe start a little larger than you feel it would be right.
I made sure that each smaller layer had the possibility to be positioned in a way that there was always at least one side with enough space for one hex base (at least). But don`t overthink it. Embrace the happy little accidents. After the first 4 hills I turned off my head and let the inspiration take me to wherever it wanted to.
When washing terrain I always make my own cheap and simple wash by using acrylic paint (mostly burnt umber), water and a tiny drop of dish dertergent. I noticed that i like the result better if I do not use the cheapest paint because the better the paint the better the pigments and the better the effect. In my area we have the German brand "Schmincke". They have a series called "Akademie acryl color". They use pigments that are very opaque. I find them to be great for washing terrain. I always make a test model before washing all the other stuff.
Hopefully this helps a little bit.
