The aluminum patio covers come in three styles. Two of the styles provided a water proof roof and one style is for shade only. The shade only ones use either 1.5×1.5″ or 2×2″ tubes places parallel to each other on rafters to provide shade.
Solid roofs are either made from one piece of metal bent into what is called a standing seam roof. This type of roof can not be walked on and on cold nights condensation can build up on the bottom side and drip on your patio. We do not install many of these roofs. However, we do like the foam roofs. These have about 3.5″ of foam sandwiched between two sheets of aluminum. Condensation is not an issue and these roofs can be walked on. Normally they are installed with a trim kit which ads some pizazz and also a gutter and downspouts.
This next picture shows a solid Alumawood roof set on a second story deck. This took a little doing getting the engineering approved through the city of Fullerton.
From a cost standpoint the aluminum normally is a little cheaper. This is partially do to the fact that it is so light and it is fully engineered for high wind conditions and come in every possible size. Thus, no engineering fees are ever involved and because it is so light weight the engineering allows us to set it on slabs without requiring a footing. We have done both as the pictures demonstrate.