Awhile back, I received a fresh set of 650b Westwood bicycle rims for the 1935 Hercules project. The original rear rim was rusted inside quite badly, and on the outside brake wear had gone through the surface of the rim. I decided that for now, I'm going to run reproduction rims. I will hold on to the originals until I decide whether I can take them to a welder to be saved. For now though, I want the peace of mind that new rims bring. I've taken pictures of the newly build wheel (closest to the camera) alongside the old.
Building a wheel is tricky, but not as difficult as you may think. Sheldon Brown has written an excellent piece on it. The article sets forth the strategy for building a bicycle wheel. Essentially, you're working with 4 sets of spokes- a pair on the drive side of the hub, and a pair on the non-drive side.
If you have done your work correctly on a wheel such as this, the spokes around the valve should create a large opening so that you can access the valve stem. Follow the Sheldon Brown directions, and you should be able to do it properly.
My build is not overly difficult, and certainly nothing innovative. My wheel involves the original, 1935 Sturmey Archer Model K hub laced to a modern production version of the original rim. The specs are very close, though the length of the spokes differs slightly, owing to slight differences in the rims.
I opted to straight gauge spokes from http://www.wheelbuilder.com/dt-champion-straight-gauge-spoke.html. They provide a straight gauge spoke similar to the originals, but in stainless steel. The originals are galvanized steel, but I'm fond of the quality of DT Swiss stainless spokes. Stainless also means no having to clean rust off of the spokes in the future, a big benefit. I went with 14 mm nipples, which matches the size of the originals. I used a "cross 4" pattern, which is the same as the original wheel.
As you can see, I have opted to retain the use of oval nipple washers. This is because the new rims, like the old, are single-walled at the holes. The washers give a little more substance to the hole areas. Modern rims often have built-in eyelets that accomplish this task. The original wheels both had oval nipple washers.