What is the easiest way to roof your garage? Build a flat roof! A flat roof construction is not really flat - it is actually a roof with a gentle slope; just enough to let rainwater drain away. Some roofs are made to look completely flat, by building a parapet or edge around the perimeter of the slightly sloped roof, essentially turning it into a sort of shallow basin. The water is then drained away into a downspout in one corner of the roof, by means of the roof forming a two-way slope. This type of roof looks flat, but is rather complicated and failure-prone, so even though it is used a lot for commercial buildings, it is really an architectural dead end for homes, in my opinion. It is better to accept that a slight slope will be visible, and get a safe and functional roof in return.

How is this sort of roof built then? First of all, it is only usable with certain roofing materials, mainly corrugated roofing sheets of plastic or metal, and roofing felt. The reason being that these materials can be laid out in a way that is either waterproof or capable of being near-waterproof where two sheets overlap. Other materials, like clay roofing tiles, need a much steeper roof pitch angle to keep out rain and snow, and so can not be used for a flat roof. Usually the manufacturer of your roofing material of choice specifies a minimum roof angle for their products, so I suggest you either follow that or go for something slightly steeper - just to be on the safe side. Once you know what to put on the roof, it is time to think about the underlying construction that will carry the weight of the roof and create the needed angle. A roof is made up of roof trusses, which give the roof its shape or "profile". They span the building to be roofed, between two parallel walls, and transfer the weight of the roof to those walls. To stabilize the trusses sideways and to support the roofing material, a number of rafters or plywood decking is used. Roofing sheets are mounted on rafters, while roofing felt must be laid on plywood, as it cannot support its own weight at all. Trusses for a moderately sized flat roof (something big enough for a 1-car garage) could easily be built by an amateur out of 2x4 lumber and plywood. But don't hesitate to consult a building engineer if you're not sure what you are doing. Trusses, rafters and decking should be able to support at least the weight of a couple of grown men walking on them. Roofing sheets don't have to be that strong though. Don't forget to anchor the trusses to the foundation using sheet metal strips or the like. If you don't, you may have the unpleasant experience of watching a storm lift the entire roof and blow it off your garage!

Now get to work on your flat garage roof - and be safe!