There are rulers for different scales- more like measuing tape- that you could use. I wouldn't worry too much though, as trees, bushes, and water areas come in all sizes. Example- You cant have a tree too small and for a tree to be too big it would have to REALLY be big. For scratch building buildings you could use wood, plastic, cardboard, etc. Im not sure I answered your Question completely so let me know if you need more help.