Metal objects can cause major wireless Internet disruption, so if you have a house with a metal roof you may need to take extra steps to ensure that your wireless Internet signal is as strong as it possibly could be. You want to avoid dead signal zones in the house where you are unable to get wireless Internet at all. You can adjust your modem and router in order to get in the best position for a signal.
Purchase a wireless router with as long a range as possible. Metal roofing significantly decreases the signal strength of a wireless network in many cases, so you'll want to start with the most powerful hardware possible.
Keep any metal objects within the home as far away from the router as possible. Situate the router so it is off of the ground, and ideally near a window to escape some of the metal roof interference.
Use a wireless repeater to strengthen the wireless signal as you go through your home. The wireless repeater will also extend the effective range of your wireless network, although it will not have as great of an effect as it should, due to the metal roof.
Move all of your computers to be within line of sight of the wireless router, if possible.