Being a firm believer, even before I became ill, in Rommel's Dictum*, I have used some unusual material and methods some of which have proven very good moves. Others, less so.
Here. a few pictures and comments on some buildings.
Looking at the prices for pre-made and kit G-scale buildings, "throwing money at it" was not not going to be a viable route.
(just occasionally it can be worth spending money to save time.)
My first test piece was a little two-room Cornish cottage. This is just about due for a lick of paint after five years (better than my house has fared in the weather, really.)

The cottage is shaped out of 50mm layers of urethane insulation board, glued together.
Then rendered. The material is waterproof bathroom tile cement.
In this case I tried forming the doors and windows by making polystyrene dies and "stamping" the windows and door into the wet render surface.
It wasn't unsuccessful, and was quick and cheap but I've not persisted with that method. Finding a good inert release agent and the exact right moment in the "going off" of the render to use the stamp was a hassle.
The roof is plastic tile sheet I had around. It has not yet given up under UV exposure, though I will not be buying more plastic tiling.
Paint: exterior white matt, and acrylics.
A few slate chips were added to give "real stone" look in places, as can be sometimes been seen on the real thing.
Another thing not persisted with, as adding a little extra tile adhesive, or milliput, and shaping and painting for details proved a better route.
Cornish engine house:
Basic structure shape carved in urethane foam.
(about 2/3 proper size, but fits well enough in proportion to the "compressed distances" of the railway.)

In location on mound, which serves to restrict view of end loop.
Again waterproof tile cement as render, this time worked a little more to give a rough impression of stone and brick, accentuated by the acrylic paints.

Here, weathered in after a few years, plant growth bedding it in more, too.

The chapel, and the pub, next time.
Some different techniques.
Chris
*"if you have a difficult job to do, give it to a lazy man. He will find an easy way to do it."