" . . . I don't want to be unsafe while trying to learn. "

The only real way for it be "unsafe" while learning to roll is if the skirt is too tight and can't be easily removed during a wet entry.

If it's too loose, it'll either leak a bit or just pop off. Either way, all you do is get some water in your boat. And actually, it's almost easier (or even more easy) to roll a boat that is full of water. It's a bit slower on the rotation but not difficult by any means.

Sean