Questions about buying a frame

I may have the opportunity to sort of build my own bike, because of a friends misadventure with UPS. Her frame is wrecked and she has suggested that I could buy the components from her from that bike and then buy a frame. I may need to buy a derailiur as well.

This is an approach that I'd never considered...how do I think about this? What do I need to consider?

That's a wonderful way to go.

You'll need a local wrench to assemble the bike bits, often it's the same shop that sells you the frame. What frames are you looking at?