Step 1: The initial plotting
The first thing I needed to do was decide how big I wanted to make the board, so I could plot out how big to make the pieces and such. I was trying to decide between having each square be 1.5" and 1.25" to a side - the red outline in the picture would, of course, be for the 1.5" squares. I'm pretty proud of how I did this (graph paper is your friend, folks!), especially with the overlapping and such.
Step 2: Piece-planning
And so I did.
(I may have adjusted some of these heights later on. I can't quite remember. Damn you, lousy medium-term-memory!)
I realize that it's silly to draw out a box for each and every piece since, in theory at least, all of a given group (i.e. pawns) will end up being the same size. I did it anyway to help myself keep track of what I'd done, and where, and such.