Malcolm Z says:

You should first try to decide what you want to do with your layout. A layout that maximizes operating/ switching opportunities will probably not look like one where the emphasis is on scenery and watching trains run through it. Do some reading; Armstrong’s books on how to design a layout for various purposes is a good place to start (Kalmbach books). There are dozens of books with hundreds of layouts. Get some of those books, they may help you decide what you want to do with your model RR, and you will certainly find plenty of ideas. One of the great pleasures of model RRing is creating your own layout to fit in the space you have, to accomplish the things you want your RR to do. Get yourself a big pad with a grid on it. Then let your creative talents flow, guided by what you have read. You will find out about how to compute grades and figure out what radii your curves should adhere to. But you are going to have to invest some time reading to make the most of the space available and your budget.
— Malcolm Z