some white cardstock, a pencil, hot glue, and
my son's left over legos (I had permission to use these) :).
I freehanded a faint outline of his initial onto the cardstock, then used my hot glue gun, small lego pieces and started gluing away.
This was my first draft. I felt like it looked too skimpy.
So I did a lot more filling in and even layering some of the lego pieces.
My advice on this project (after the fact): Use a standard font for the letter. At first I thought I wanted a slanted cartoon-like letter shape but after the first draft (above), I realized that a standard font would look better. Start with larger pieces and create the outline of the letter first, then fill in. Vary the pieces, don't line them up. Stick to 2 - 4 colors. Don't bother with the glue strings until the end, then you can pluck them off.
Here it is in my son's room. He loves it!