I'm looking at a new roof for a townhouse (duplex) of which I own both units.  

ALWAYS seek a lawyerDon't forget about Home InspectionTitle PolicyAppraisalConsider obtaining pest inspections, a roof certification, home warranty plan and hiring other qualified inspectors.

In fact I just did some drywall work and patched a roof because it was leaking.  

Are there any window options available that can actually deal with the fact that basically there is no roof (or at least no overhang) to protect against the elements?

The problem here is contractors, for example window replacement guys from big boxes, will test and if positive your install price wtill go through the roof because they have to wear suits, tape off and sheet over everything, etc.3.

If you need to replace the roof do you walk away?

From the outside I can tell the roof is new (installed <6 months ago), the building needs to be painted (lots of peeling already), some window screens need to be replaced.

We have been looking and although I am not complaining because I have a roof over my head.

Square the back, fancy the front, 2-3 ridges on the roof and all hip with a gable on the front.

The roof was redone in 2009 and the seller have agreed to leave all appliances except the washer and dryer.