One of the biggest problems with making terrain is the fact that it tends to eat paint in large quantities, well at least in comparison to figure painting. Even a small building or hill can seriously deplete a pot of paint and at current prices that can put a crimp in your pocket very quickly. A good solution to this is to use the paint testers you can get in any DIY store. They come in nice large pots very only a couple of pounds, and being emulsion you can water them down (usually a good idea as they can be very thick). These days you can even get them in a good range of colours or get them mixed to order if you so wish (colour matching your terrain to the colour you’ve used on your figure bases always looks good).