How many kW are you planning to draw?  It can be anything from easy to impossible depending on your answer.

Keep in mind that commercial leases require you to restore the building to original condition if the landlord wants.  Cutting holes can get pricey.  And leasehold improvement laws mean that any electrical work you do stays with the building.

For any scale that I find interesting these days this means buying the building.  Most upgrades to make a building suitable for serious mining will cost more than the property itself.