What are the merits of setting up your own facility, particularly if you can access cheap power, vs. paying for a hosting service?
Hosting is generally risky due to a few reasons that have been discussed in depth here, but mainly, it's the host's greed that could screw you, if the market conditions are bad, and the ROI is way too long, the host would be happy to have your gears running, at some point, when ROI is very short the host would rather run his own or charge you more because, for one, they would know you now make more profit and two, because they can.
This isn't the case with every host but if you read all the stories you will find more sad endings than happy ones, in general, you should always try to avoid hosting.
As for building your own infrastructure, it really depends on what your budget is, I think if it's not a few million $ -- you won't be able to build anything that would have a great ROI, simply put, there is some common cost which doesn't differ much between running say 100 miners and 500 of them, splitting that cost between 500 vs a 100 would make a huge difference.
A middle ground would be renting a warehouse/hangar/land with a long-term contract and sourcing power directly from a power provider.