Newman Atkinson says:

Garland, For a shelf layout run, Most modelers will build their own. Sometimes brackets you find at hardware stores have a tenancy to bow down a bit form the wall. What you really want is a triangle frame that is square on the top support and also has a good angle brace coming from the bottom of the wall support That brace keeps the top support level where a metal wall bracket has a tendency to bend down under weight. Sometimes the guys will use a longer wall board to go down closer to the floor and do the triange bracket half way up the wall support to hold th that top support level. Many times a layout will need a support that comes out a foot like for a hallway shelf and other times one that comes out 2 or 3 feet like to support a yard. Then on top of these they set the stringer length boards to lock all the brackets together and build from there.. from Newman