The built-in amplifier will not clean up the signal. It will amplify the noise along with the signal. The appropriate solution is a larger antenna with an increased amount of gain. Bi-directional means the antenna is equally sensitive to signals coming from the front and backside. A Bi-directional antenna is more susceptible to ghosting because it can't cancel a signal reflection coming from behind.
Outdoor antennas are always better than indoor antennas.
The mechanical details of an outdoor antenna installation depend upon the selected antenna and the available site. Shops that sell rooftop antennas offer a wide variety of hardware to secure the antenna to any structure. Consult with the shop's sales staff to select the appropriate hardware for your particular situation. We encourage you to have your antenna professionally installed if you feel uncomfortable about working on a rooftop. Here are a couple of general comments about antenna installation.