In general today, prebuilt wheels are less expensive. The allure of building your own wheels is that you can customize them any way you want, and the pride of riding on your own craftsmanship. I don't know anything about the no-name carbon rims, but do you have any experience with tubulars? What do you plan on using them for? In my personal opinion, tubulars aren't worth the hassle (fixing a flat is more involved than clinchers) for everyday riding, but are great for racing.

Post your weight and intended use for the wheels to get better recommendations.