Unfortunately for games like Frostgrave (Mordheim, Infinity)' when designing a terrain board, more is more. Think multi-level, think taller than a miniature at minimum, think alleyways. Follow the rulebooks guideline:
"Remember, the ruins of Frostgrave are crowded and maze-like, so there should be lots of terrain on the table, and there should be few areas where line of sight extends more than a foot or two, if that"
Here is a horrible pic of my 4x4 work in progress table:

I need some more elevated areas like the church, and bridges to span them (and ramps, and ladders, and makeshift platforms) before I feel it will be a good table to play on.