There’s no rule so you can do it either way. I generally do it with the fabric folded so that the wrong side is out and the right sides are together on the inside. You can see an example of me doing a pattern layout in this tutorial. I think I do this as a habit, because commercial patterns present their layout in their pattern directions this way. I’m trying to think of an example where it would really make a difference. The only example I can think of where you would really want to lay your pieces on the right side of the fabric is if you were working with a directional print of some kind, like a plaid, and you were trying to match your pieces so that everything lines up perfectly in your finished project. And some fabrics like wovens or fleece look exactly the same on both sides so it’s pretty much impossible to tell which side is the right or wrong side without looking at the selvage holes. In cases like this, I just designate a right side and try to keep everything consistent so I don’t run into problems later.