There are a number of plans for matchbox pinhole cameras out there. Here is one. Link

If you want fall off you just need to have a big enough piece of material behind the pinhole to get as much of the image circle as possible. Also a cylinder will give you less fall off as you are keeping the film plane distance from the pinhole more constant. You don't actually get in and out of focus areas with pinhole, that is a characteristic of lenses. Have fun!