you can go to www.usps.com
and you can get see the shipping prices there.. (find where it says calculate shipping)
you put your zip there zip what kind of package you will be shipping & weight and it will tell you everything.
now when they pay you through pp all you do is click the print label button and fill out the rest of the info which would be how your shipping & weight now for first class or flat rate boxes you do not need to measure the packages ... for priority & parcel I belive you do.
now if they gift you the money or if your just sending something like say a gift you will have to do multi order shipping .