Actually, it will wrap funny as a rectangle. Years ago my mom showed me how to make a wrap around skirt without a pattern. I still have it... And it was super easy to make.
I used a newspaper to cut out a pattern, so that I could cut out the fabric. The wrap skirt consists of 3 isosceles trapezoids (wait, what?! I thought I'd never use geometry in real life!... It just means that the two non-parallel sides are the same length, and have the same sized angles to the two parallel sides... see here for an example of what one looks like http://mathworld.wolfram.com/IsoscelesTrapezoid.html
Use a measuring tape to measure around your waist/hips where you want the skirt to hit. Figure out how big around your hip/waist is at that point, and then add half of the number to your measurement. So, if your measurement around the hip/waist is 36, add 18 to it, to get 54 (feel free to fudge around with the numbers a bit to make the part that wraps over wider or narrower, as you see fit.) Tack on another 3 inches for seam allowances (1/2 inch seam allowances). So, now you'd have 57.
Calculate 40% of your hip/waist number. In this case, 57 x .4 = 23 (rounded up from 22.8.. just round to the nearest whole number) Then figure 30% of the hip/waist number. So, 57 x .3 = 17. (rounded down from 17.1)
Decide how long you want your skirt to be, and then tack on another 1.5" for the top and the hem. Let's say we want it to be 18" long. So, our total measurement should be 19.5.
You'll want to make three, equally sized trapezoids with 17 inches on the top, and 23" on the bottom (or whatever numbers you came up with). (Remember, you want the trapezoid to be symmetrical, so that if you folded it in half, the two non parallel sides would match... the easiest way to do it is to draw a rectangle on the newspaper that is 17" by 19.5" (or the shorter, top of the trapezoid, by the length of the piece). Then subtract the number for the shorter side of the trapezoid from the larger side (23-17=6). Extend the bottom part of the rectangle by 3 inches on either side (half of the difference between the top and the bottom). Then, draw an angled line connecting the end of the 17" line to the end of the 23" line, on both sides. You should now have a trapezoid that looks like the one in the link up above.
Here is the backside of my skirt, so you can see (ignore the extremely crappy stitching. This thing was horribly put together, mostly by hand...)
Make three of these with the newspaper, that are all of equal size. Lay these out on your fabric, and cut the fabric out.
You'll assemble the pieces so that all three are lined up next to each other, except the trapezoid in the middle will be upside down (so the longer end is on top, and shorter end on the bottom). You should find that this gives you a really, really long trapezoid.
Like this: (Ignore my pile of shoes, and messy carpet!)
Next, stitch the pieces together, allowing a 1/2" seam allowance.
Hem in the sides and bottom, again allowing 1/2" seam allowances.
Now all you have left is the top. Hem over 1" of fabric, but make sure that you leave enough space to put a ribbon through, to tie it closed.
Once the top is stitched down, thread a long piece of ribbon (2.5 times the width of the top of the skirt, at least) through the top hem.
Wrap around your waist, and enjoy!
(Crappy picture of me, with the skirt thrown over a pair of jeans... I'm sure your final product will be much better than mine was... keep in mind it was one of my first sewing projects)
Of course, you can adjust it however you like to suit your tastes. You can make it so that the end of your finished skirt has straight edges, instead of slanted ones. You can make it longer, or shorter. You can work it so it's wider at the bottom. You can make it longer (try adding more trapezoids for a skirt that wraps around more than once).
I hope this was clear. If you have any questions, feel free to ask.