The floor structure of an attic is also the framing for the ceiling beneath it.
Attic support structure.
Attic and roof structure inspection your home check.
Depending on the roof covering material either horizontal laths battens or purlins are fixed to the rafters.
Collar tie used for adding additional support to attic roof supports.
Addition of engineered i joists.
This is made up of ceiling joists typically 2x6 or larger boards.
Or boards plywood or oriented strand board form the roof deck also called the sheeting or sheathing to support the roof covering.
This photo indicates a properly installed knee wall in a attic for additional support to roof structure.
Typically ceiling joists are 2 6 or 2 8.
This attic structure needs additional support and was most likely repaired by a non professional.
More times than not the floor structure of an existing attic is actually a ceiling joist.
Depending on your attic structure an engineer may recommend the installation of lvls between the existing joists to bring the floor structure up to code.
They are designed to carry only the weight of the drywall or plaster depending on the age of your home.
As long as they are not damaged the joists should be strong enough to allow you to move around in the attic for an inspection and to provide storage for typical boxed items.