I was looking at getting the West Elm Rectangles Day Bed, however, the bed was a bit too tall. The window sill of the room was 26" high and I didn't really want the bed above the sill. I found the plans on this site and decided to modify the plans so that the top of the bed would be flush with the top of the sill.
To make the bed fit, I removed 2" from the height of the rectangles (10" cuts instead of 12") and 1/2" from each of the top and bottom joiners (1 3/4" cuts instead of 2/1/4"). Finally, the corener legs are each cut to 26" instead of 30". The makes the be 7" off the floor instead of 8". Overall, I'm really happy with how it turned out.
A couple of things I learned:
1. I used clear pine for the wood. It was very smooth to begin with, so I didn't need to sand it. I primed all the wood prior to cutting.
2. The pine was not all exactly the same size. This means that I could only have one side completely flush and needed to decide if it was the inside of the outside of the bed (I choose the inside). I sanded the outside a bit, but all the pieces still weren't completely flush, but I didn't care since it would be facing the wall. You may be able to get better results with more expensive wood.
3. Get a Kreg jig. I bought the pocket unit for ~$20. It was very useful for creating joints. Make sure to do a test joint as I initially set the depth incorrectly and drilled too deep (luckily I DID do a test piece)
4. I did not buy the Kreg plugs. Instead, I just used wood filler. For each hole, I covered with wood filler, let dry and sanded. I then put on a second coat and sanded again using 300 grit sandpaper. You can not tell there are any joint holes, and am very pleased with how the joints look.
5. I did not use the Kreg Jig on the 1/3/4" top/bottom rectangle joiners, I just used 3" wood screws and screwed throught the top/bottom in from the top/bottom. I used a Big Gator Drill Guide to drill a pilot hole that was perfectly perpendicular (as I don't have a drill press) prior to screwing the pieces together. Filling the holes with wood filler and sanding (twice) worked well.
6. Sanding!! I sanded a lot to get the paint to be very smooth. It was a bit of a pain as I did it all by hand. I think a belt sander might have made some of the sanding go a bit quicker, but the rectangles day bed has so many inside areas to sand, you're going to have to do some by hand.
7. I used a primer on all surfaces and sanded the primer smooth prior to the final coat(s). For painting the final coats, I used a foam brush as the paint was pretty thin and I did not want to see any brush marks. I considered spray painting the final coat, but it was just easier to do by hand.