In a roof truss, the roofing material is supported by : 

Explanation:

Purlins:

Purlins are beam members that carry roof sheeting (or roof material) and are supported by trusses, these run parallel to the ridge and connect the trusses along the length of the ridge. In other words, the beams that carry the roof loads in trusses are called purlins. 

Principal rafter:

The principal rafter is a top chord member in a roof truss and boom is the principal compression member in a crane. The principal rafter of a roof truss is designed as a continuous strut.

Bottom Chord:

The horizontal (and inclined, i.e. scissor trusses) member defines the lower edge of a truss, carrying ceiling loads where applicable, or members that extend from one support to the other through the apex are called the lower chord. This member is subject to tensile and bending stresses. On a simply supported, non-cantilevered truss.

Hence option (2) is the correct answer.