You have a few options. You can buy or rent a facility designed for use as a datacenter or space in one (many of us just rent a caged in section of an existing datacenter) or you can buy your own equipment and make a warehouse or your office (or bedroom) a co-location facility.
The most sensible option for starting such a facility would be to ge some cage space in a reputable datacentre, and get your own bandwidth lines in. You effectively have your own DC within a DC. Much more practical than setting up your own facility to begin with.
That's the way to start. Many of the bandwidth providers in established data centers will take care of such things as routing and dns for you. We've looked at building our own data center a couple of times and unless you're hosting a couple hundred of servers it's really not cost effective. I would even venture to say even after a couple of hundred servers it's not worth it.
Get yourself going first and get a good reputation. As you grown then you can add your own services such as routing and stuff.
Atlanta, GA and Las Vegas, NV. Colocation
In my opinion, if you can't handle DNS and "routing" on your own, you are not prepared to handle dedicated or co-location customers; and should stick to reselling the services of a vendor who has the requisite technical know-how to serve their clients effectively.