It may seem quite simple and quite honestly I was debating about even writing this article. I mean if you are going to go through the trouble of installing metal roofing materials, you should know what you need as part of the job. However, my lovely wife encouraged me to go ahead and share this information since you never know who might find it helpful. So if that “someone” is you…I sincerely hope this helps you out. So to start out, if you are planning on installing new metal roofing on your home, shed, or outbuilding the roofing screws are the most vital part of the job. It is very important that you choose the correct screws to use as there are significant differences between normal screws and those intended to hold roofing in place.
When you are working with metal roofing, gaps are often created when the screws are put into place and this can cause some damage in the future. It is therefore very important that you buy screws that have rubber caps on the tops or that come with washers so that you get the correct seal. The roofing screws with washers already have the washers integrated and they are made of rubber or plastic. These will prevent your roof from eroding and rusting over time due to water seeping into the open spaces and causing damage. You must take care that you do not place the screws too near to one another or too far apart either.
The screws are inexpensive to buy and you can generally purchase a package of five pounds worth of two-inch long screws made for use on metal roofing for around forty dollars. They can be purchased at nearly every large home improvement store or if you have a huge project, you may be able to buy them directly from a local roofing company at their cost. It certainly doesn’t hurt to ask.
When actually screwing the screws into the steel paneling it is generally best to leave a space of between one and one half to two feet between the screws and not more.
It is not recommended that you attempt to manually drive the screws into place with a hand held screwdriver as it is a very difficult task to do and will be nearly impossible to finish in this manner. There are battery powered screw guns on the market that are made for driving roof screws but you will need to re-charge the batteries at least hourly which would waste a good deal of time. The easiest way to drive the screws into the roofing is by using an air gun that runs on compressed air or an electric drill with a screw tip on it. These guns are safe to use and will give the roof a fine, finished look. 
The length and style of the roofing screws you will need depend on what type of roof you are installing as well as where on the roof they are being used. When you are laying the roofing over the top of a layer of asphalt, you should use a three inch long screw. In the case that your roofing does not come with pre-drilled holes then you will need to use a self-tapping variety that will make getting through the metal easy, quick and with less chance of an injury occurring due to the screws breaking. The self-tapping type are ideal for the general areas of the roof as well. For attaching the first edge of the roof down, a one-inch long screw will suffice