I always try to build rather than "buy off the rack", for the following reasons:
1. I take a lot of pride in catching fish on a rod that built and on a fly that I tied.
2. I like to use better/different hardware than manufacturers do on stock rods.
3. I like to save money.
Not to say that my rods are better or worse than stock rods, but I feel that my enjoyment of them is greater because I took the time to hand craft them.