Just trying to clarify the requirement, as the options are different

A lot will depend on your (and your team if you have one - if not you will want to get one) ability to manage servers, switches, networks, routers etc

The "simplest" way to provide dedicated servers (and vps etc) will be to partner with an existing *actual* provider of those, and to effectively resell under your own branding.

You will be required to provide the support, and (unless you arrange otherwise) the management of those - and I would *STRONGLY* recommend picking a provider with a proven track record of uptime, with their own network and AS number. It may be better to get them to do the management as well if you dont have your own people (inhouse or outsourced) to be trusted and competant to do that.

Essentially, you "rent" the servers from them, and then sell them on to your clients (with appropriate mark-up inline with the additional value you are adding to the equation)

The next "step up" method would be to arrange rackspace/colo for your own servers in a datacentre and for you to rent out those instead

Which of the above you feel comfortable with is a balancing act between relying on a 3rd party for the servers and your own abilities to source and maintain the hardware ...