I have a 5'x9' piece of blackout cloth that I want to hang and be able to roll it up when not in use. I was thinking of buying a 10ft piece of piping to hang it from. the question I have is what kind of pipe will work. I was thinking of getting at 10ft 1/2" diameter Type-L copper pipe. Online it looks like the copper is pretty thin and I was wondering if it would have enough strength to hold up the blackout cloth with supports only at each end, without sagging in the middle. thanks!

The larger the diameter of the pipe the better. The smaller diameter pipe will mean the cloth must flex much more when rolled.

You should take a look at the DIY Tab-Tension Rollable BOC Screen thread.

You might be able to use the ideas posted there as is or modify them some to make it a top roller system.

If you can get a 2" diameter copper pipe that would be a better option for a roller.

You may find that round conduit is much cheaper though.

thanks for the info. setting aside, for the moment, the benefit of rolling over a larger pipe, would it be physically strong enough? It won't be rolled and unrolled all that often so it shouldn't be too much of an issue

The other consideration will be how stiff the pipe is.

You will also need to put some sort of bottom bar on it.