It's depends of your needs.
Method 1
If you need your own instance of CloudFoundry you can download the micro instance and use it as your private PaaS. It's a simple Ubuntu VM with services on it.
Pros:
- You can deploy it on any public or private cloud you want.
- Cheap to run and use.
Cons:
- Not all features will be available
- You will max out your VM quickly
Method 2
You can purchase CloudFoundry as service from Pivotal or AppFog. Pros and Cons are the same for these services as rolling your own.
Method 3
You can deploy the full CloudFoundry instance on top of your favorite IaaS platform (Amazon, WMWare, OpenStack).
Pros:
- All power and control in your hands
Cons:
- Can be difficult to install (I have no success with CF v2.0)
- Can be expensive to run