Bill:
I do not know of any particular book or website that deals specifically with investment in NNN lease properties. I am sure there are several of each, but do not know any off the top of my head.
I think that a good start would be in learning how the “income approach to valuation” works. This is an appraisal technique that is the preferred way to value income producing property.
I also think that the closest thing in my website in the form of a tool that can help you calculate the NOI of a property can be found at
http://www.loanuniverse.com/sensitivity.html In that page, there is a link to a spreadsheet that can help you calculate NOI and debt service coverage. Of course, I am the first to recognize that there are other more professional sites out there that have information on real estate investments, but on the other hand, there are many out there that are peddling useless information and are trying to sell you something. In other words
”be careful”If you have experience being a landlord to residential customers, then you are already ahead of the curve. Personally, I think that a commercial tenant causes a lot less headaches than the several residential ones that a purchase of that size would entail. However, remember that there is another side of the coin. If you lose a tenant for a highly specialized property such as a fast food restaurant, it will be difficult to find a suitable replacement. The thought of “all your eggs in one basket” comes to mind. You really need to have someone go over the lease.
Good luck