This pretty tutu was made for my pretty little dog-niece Zoey. My inspiration for it was this little pug, but, I have to proudly say, I made this incredibly more cheaply than I could have bought one. It only took about a yard of tulle and some left over elastic.
To make it measure your pup around the belly and cut a piece of elastic (I used 1 inch wide) to that length. Don't shorten the elastic to compensate for the stretch because by the time you're done it won't be very stretchy. Measure from belly to bottom and cut out several strips of tulle that are double that width. Fold the tulle in half and sew the folded edge to the elastic, doubling over the tulle in random spots to make it poufy. It helps to leave a little of the elastic bare on the ends (a few inches on each side) so that you can better sew the elastic together at the end. Keep adding pieces, sewing each over the next, until you have a nice poof. Trim your edges up nice and neatly.