Hi Al,
The ability to efficiently and effectively process a potential rehab, renovation or remodel of a building is an ever evolving art. Whether the structure was built in the last 10 years or 100 years ago or more, the potential for hidden secrets is there. Warning signs are always present and with time and experience we become better at seeing below the surface. There are also issues that lie on the surface but without special knowledge they can be easily overlooked. There's also the cost factor to consider for labor and materials in an industry that's forever evolving. And, we can't forget the ever present building codes and zoning regulations. Over time we can learn to depend on our abilities that come from experience. In many cases that experience comes with a price. The price of trial and error. In many cases it's more cost efficient to hire others who can apply their special knowledge and save you time, aggravation and money in the end.
With that said, one thing I might suggest is to take a look at the (HUD) inspection checklist. It's a standard form that's available on-line. The form can be modified to address the inspection of most any size or type of building. The form can be applied before, during or after construction. Using the inspection checklist format allows you to stay on track and take note of specific details as you proceed from one area of concern to the next. It's a tool I've found helpful to keep from being distracted and missing costly details.
Another suggestion would be to take photos, take plenty of photos. Many times having the right photos can save you a return trip or serve as a quick method of answering a question you or a contractor might have.