I do much the same thing. Generally speaking (at least for Remo heads) the head comes down 10/16" (5/8") from the bearing edge. I usually but the lugs back on and tighten the head down a bit to get an accurate measurement. 10/16" + 10/16" = 20/16" (1 1/4"). So I usually cut (or have the supplier cut) the wrap 1 1/4" inches shallower then the drum. For example, for an 8" depth drum, the width of the wrap would be 6 3/4". Be sure to get the correct measurements for your specific drum. This works well, and leaves the entire area where the head sits on the unwrapped part of the shell, which fits looser and has more room to vibrate, but when assembled it is completely unnoticeable, because it is hidden by the hoop and head. You have to be very precise when you wrap this way, but you have to be very precise when you wrap a drum regardless.

What I do is similar to the above method from Mutant Mozart: Make small "dashes" with a marker along the outside of the shell 10/16" (or whatever your measurement is) in from the bearing edge all the way around, marking every few inches, then just line up the wrap with these dashes and you're good to go. I do this step with the head off and a tape measure (after I've already gotten an accurate measurement with the head on and tensioned)

As a tip, once you are ready to wrap the shell (if you are glueing) is to put some painter's tape between the dashes and the bearing edge, so you don't have to worry about dried glue on the bare part of the shell (after wrapping). Dried glue is a pain to get off of bare wood! Another tip: It is easier to remove the tape when the glue is still wet. Make sure you get the glue all the way up to the dashes on both sides, so that the top/bottom of the wrap will have good adhesion.