Hi, Mister Duck, welcome to the Gauge.

I'm afraid that I can't recommend any books for scratchbuilding, as, if I want to build something, I just go ahead and build it. I have a lot of years of trial and error behind that ability.

Railroad Model Craftsman magazine has been running an ongoing column, for some months now, on various aspects of scratchbuilding, which might give you some insights or ideas.
My suggestion to you, whether or not you find the books for which you are searching, is to purchase an N scale ruler. Most sheet products, particularily styrene, are measured in thousandths of an inch thickness, whereas most dimensional stock (strips and shapes) are measured in fractions of an inch, such as 3/64"x1/32". Some materials may also be measured in millimetres. A good scale ruler will have scales for most of the major scales: N, HO, S, and O. It should also have an "inch" scale and also one in millimetres. This will give you some means of comparison when looking for suitably sized materials for a project.
Wayne