As Dave Loudin says, the Youngstown stations are pretty strong at your house, but barely receivable at your friend's house.
If your friend tries to add a second antenna pointed at Youngstown, they will probably get WNEO, but WKBN and WFMJ are probably going to be very flaky. WYTV is probably not going to come in at all. In other words, the added antenna is only going to get them 1 more channel reliably, and another 1 or 2 channels might appear from time-to-time. Is it worth it? There are occasional differences in local programming, but most of the time, the network shows will be the same between markets.
For flat roofs, you can use a sled mount (like
this). These use cinder blocks or similar heavy objects to hold the sled and mast in place. You should use rubber mats underneath the sled to avoid damaging the roofing material underneath.
For sloped roofs, you can install a tripod (many types and sizes to choose from). The feet of the tripod get bolted directly into the studs in your roof. The tripods are usually positioned somewhere along the apex of the roof so that the mast can stand vertically. Weatherproof sealant should be used around the areas of roof penetration to minimize the chance of leaks.