Another important matter to consider is how the roof is built. It is important that a roof structure be well adapted to the frame that is supporting it.

In the German tradition, roofs are generally classified into 3 Categories: Sparrendach, Kehlbalkendach, and Pfettendach

A Sparrendach is a roof structure that relies on the rafetrs (Sparren) to bear the load of the roof. This may refer to clear span rafters with no trussing action going on, or it may involve minimal trussing. The general rule the germans use is that a Sparrendach is unsuitable for any slope shallower than 30 degrees.

A Kehlbalkendach is a roof system that adds collar beams to the rafters. For larger spans, purlins can be placed under the collar beam to provide additional support.

A Pfettendach is a roof that uses purlins (pfetten) to directly support the rafters.

Trusses are rare, and are generally more in the category of light trusses when they do appear. Common purlins are all but unheard of. A truss roof is referred to as a Dachstuhl, but Dachstuhl can also be used to refer to a system of purlin support framing.

the 4 most important roof types to know of are the Einfacher Kehlbalkendach [simple collar beam roof] Stehender Kehlbalkendachstuhl [collar beams supporting by direct-posted purlins] Liegender Kehlbalkendachstuhl [collar beams are supported by purlins which are supported by inward-canted posts, a cruck-like construction very common in Switzerland] and Stehender Pfettendachstuhl [directly posted purlins that support the rafters, no collar ties]
pictured in order from the last paragraph: