The type of aluminium best for windows is thermally insulated profiles, typically using a polyamide thermal break, the latest generation insulator, creating a thermal bridge between the outside and inside profiles. Together with the double or triple-glazed glass in your aluminium frame, the thermally insulated aluminium profiles create an energy-efficient window. Another benefit of thermally insulated profiles using polyamide is you can easily have windows with a different colour frame inside and out.
Of course, having decided to build with an aluminium frame profile you will have to decide what shape you want. As previously mentioned, this is the strongest material but it is also one that are not as widely available as some of the other materials. Therefore, you may find that it will be more cost effective for you to build with some form of shed roof. However, before you do this you should think about whether you actually want this feature or not.