It was lengthy, and costly for the owner, but now (over 5 years later) has very stable, long term tenants in clean, safe, secure, and updated apartments.

Your point on the lease length is well taken.

The question as phrased can lead to a rather lengthy weighing of pros and cons that you should be discussing with your attorney, your tax advisor, and your insurance broker.

My recommendation would be to make sure you have a lengthy track record before doing one. 

It's super lengthy, permit-intensive, and cost prohibitive to add value in these ways in MOST situations.Ultimately, unless you have a building inspector come out and literally spell out for you what you need to do, it's going to be really difficult and time-consuming to identify everything the property will need to confirm that additional living space.   

@Danny JimenezThe contingencies are usually boiler plate in most contracts, the length is just determined for each.

For the last year or so, almost all my defaulters are coming out of lengthy forbearances, cannot self correct and are headed to foreclosure and must sell/short-sell.

You're looking at the likely peak of a lengthy upswing right now.

They intentionally make the process lengthy and difficult, maybe to justify the head counts in the city departments.It will not be a surprise when one planner approves a design, but next day another planner says no.

If you have made it through the rather lengthy post, then you must be interested in me in some way (or you're just bored going through BP).