I am propagating succulents, mostly sempervivum, and am having problems with the Arizona sun and temperatures.
I am builing a pergola to help protect the plants from the direct sun and need to know the % of shade cloth I can use that
will not cause problems with the plants. My babies have been frying!

Puzzle: Gee, I don't know what the percentage is for the shade cloth that are on big rolls in the big box stores. You can buy them by the yard and just have the guy cut the amount needed. If you want to buy your own roll, just look for the same kind of shade cloth (that's on the big roll) in the ready made packages that's pre-measured like 6ft X 15 or 20 feet. That's how I buy my shade cloth. I think I once bought the 6ft X 100 ft roll and used it to shade the top part of my tall windows.

Here's an example of packaged one sold in BBstore:
http://www.homedepot.com/p/Eas...

I think the more blockage of sun that the cloth can achieve might translate to more cost. I would assume you just want some protection from the sun, not total blockage of sun.

I'm seeing the same problem with wicked Kansas sun.
I can't give you an exact percentage for cloth, but have tried planting some semps in areas that only received morning sun. I have been pleasantly surprised, since I thought those areas didn't receive nearly enough sun, but they are doing quite well.

I guess my assumption about how much "full sun" semps actually need was off.

My understanding is that "full sun" means 6 or more hours a day of uninterrupted sun. In Arizona, 50% shadecloth will still yield the equivalent of 6 hours a day of sun (because, in reality, everyone's sunny days are much longer than 6 hours this time of year).

If you are in doubt, call your extension service.

Puzzle also I have found that especially when young they want bright light, but that doesn't mean full AZ sun!! It is a bit deceptive I think! I've also noticed that around here (Seattle WA) they want that full sun in winter more than in summer! Just my personal observations! (after growing semps, I don't think they really need full sun, I think they do fine in it but also thrive in part sun!)

Mine are all in full sun year round. But Arizona sun is much different and would be very detrimental to semps.
My daughter lives in New Mexico and grows her under a tree that provide bright light, but not direct sun. They have done very well.
I agree with Kate's idea of the 50%

This is the one I have been using for several years now. https://www.growerssupply.com/...