How hard or easy are Zipp rims to build up? I have a set of Zipp 303's, but I want to rebuild the rear wheel with a new hub.

I've built many alloy wheelsets before, the last was with Kinlin Xr-300's, but I've never built a carbon wheel. I read the building tips on the Zipp website and they mention lubricating the nipple shoulders, what type of lubricant should be used?

Also, I have hear that Zipp rims are made specifically for front and rear so you can't build up a rear rim as a front wheel and vice versa, true or not?

Those rims are very easy to build - because of their stiffness. It also means you can have a very horribly built wheel and still have it true - e.g tension all over the place. On the Zipp website there is a live chat link - they will be able to easily answer your questions officially.

Only twelve years late, but never hurts to reply:

As Operator said, Zipp rims are great fun to build and tend to be very forgiving. I'm not sure what type of lubricant Zipp would recommend using on nipple shoulders. For my builds, I'll coat spoke threads with a small amount of Phil Wood grease for assembly, and then give each nipple a drop of Tri Flow after everything is put together. Probably overkill, but I enjoy the process and it's worked well so far.

I included process photos of the first Zipp wheel I ever built. A 20 hole hoop laced to a DT Swiss front track hub. The spokes ended up being 286mm using a 2x pattern.

Cheers and best of luck with your builds!