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You're using the hardware cloth down low to prevent reach through predation, right? So figure about chicken height, at least. Some people just go ahead and use the 3 foot wide wire all around the bottom of the pen, horizontally, so they don't have to cut the wire except on the ends. Also, if you have any roosts or any other areas in the run where the chickens could come close to the wire, block off those spots, too.
For an apron, I would build it at least 2 feet wide, and even more if I was counting on it to keep critters out at night.