I think most people follow the plans and construct the tips so the upper surface matches the wing profile and the end is the 45 degree bevel. This is done by attaching the tip stock with a short side (adjacent to the right angle) to the tip rib.

I chose to make mine more conventional and attached the long side (opposite the 90) of the tip stock to the tip rib and shaping the tip like a conventional wing tip. I've got a picture of the (almost) finished result in [link=http://www.rcuniverse.com/forum/fb.asp?m=5661736]my build thread[/link] If you look through the entire thread, there are a number of pictures from other people showing wing tips that might also help...