I've done this before.
The way ours worked is everyone picked the block or theme that they wanted. You could add some fabric in the box if you wanted, some did to maintain consistency. I picked one block and included the pattern for the block, wanted it scrappy so did not include fabric.
Here is what I learned;
The quality of some of the fabric (and I'm not that picky) was... umm ....... not so great.
Everyone's 1/4" seam allowance was different so I ended up adding a 1" border on all of the blocks to square them off.
One of the ladies chose a detailed pineapple block to do in black and white and provided the paper pieced template only to realize that half of the blocks had been trimmed and the last seam allowance was now gone.
So my advice is to choose a pattern/theme that is forgiving and do it for fun, to have a quilt that your friends have worked on.