After drawing the desired design on graph paper, go through each line and edit image, adding or removing lines to make the table the right length. The table can be more than 500 lines long. (Hint: the easiest way I've found to do this is to copy enough 'B8(00000000),' lines to fit the size of your design, then enter in the 1's in insert/overwrite mode, which almost all text editors have). If this seems a little confusing, try opening up minipov.c to see how the minipov message is made.
Generate the table using Repulsor's handy website! Just copy it into your mypov.c table.
Or this one that will make largeimage.c with a custom text message, just rename it to mypov.c when you save it to use the above instructions.
If you're running windows, Magician Soft has written their very own POV message generator! Awesome!