The main difference between these tools is the type of nails. Roofing and siding nailers may look similar, but the first one is used to put the shingles tightly together, and the second - for siding stuff. That means the nails for siding nailer should be stronger. However, the roofing nails are usually bigger because they need to cover a bigger surface. The length depends on the type of roofing shingles.