I like to make a box of known dimensions with the Marquee tool, Fill it, give it a stroke, then alt-shift-drag it to one side to make a copy. I fill the copy with the second color, merge the two layers, then alt-shift-drag and merge again. That makes four boxes with alternating colors and a stroke.

You can set the Marquee tool to a fixed size by changing the Style from Normal to Fixed Size. The stroke should go to the inside of the object, and each box should be wider than you actually need it to be so that when you overlap them to make the strokes all the same width, the boxes are the correct length. This is important because the neatline serves as an additional scale and must therefore be as accurate as the main scale cartouche.