This means the roof usually. Typical mounting sites are the chimney, the side of the house where the roof peaks, and directly on top of the roof along the ridge. Installing a rooftop antenna can be dangerous. Roof work carries with it dangers of a fall, and there is a risk of shock as well. Never let the antenna or lead-in come close to a power line.
Cable is more durable, more weatherproof, and less prone to pick up interference.
Twin-wire is much less expensive and conducts the television signal from antenna to set with considerably less loss than cable. Install the lead-in line as directly as possible. Do not let it lie on the roof where it can be buried by ice and snow, and avoid horizontal runs. Use standoffs to keep the lead-in line away from gutters, drain pipes and other metal objects. Never run the line inside a drain pipe.