flooring a part of the attic will not do that much damage ifyou will. If the entire area then you might want to reconsider.
Do an area that serves your needs and the main thing is not to knotch the rafters for the wiring, this will weaken them. And too do not lay decking directly on the wiring this will slowly erode the sheathing.
Make shim spacers that will take the wiring along its course.