The 68 cutlass im working on, the owner of the car would like one of the covers that fits over the roof hood when it's in the down position to cover up the roof. What exactly do we need to order to fit one? How does it attach?
Thanks guys!

 

I think you mean what is called the top boot. It is usually a smooth type cover that has plastic tabs that slide under the stainless large U shaped trim piece at the back of the top.
On the front there is a small round bead that slides into a roundish bracket the runs alont the top of the seat back. Repro. companies sell those, check ebay or opgi.com.

 

Well, at least that's what it's called here in the U.S. Not to be confused with the "boot" where one puts luggage.

As noted, search for a convertible top boot at the usual sources.