There is a separate hydro meter run for it but it is disconnected because the owner said something about animals chewing the electrical wires in the attic.

., I would contact Animal Control in your city and explain the situation.

And negotiations has gone smoother and less costly for me ;p

I could work a deal in those if I needed to, but it's a totally different animal.. 

On one hand I can see them not being happy about that, on the other, they are staying longer and thus increasing the time the animal may do damage.

I would issue a 10-day notice to comply for violating your no animal policy.  

The dog ( service animal ) attacked another tenant baby and they sued me.

I been reading about single family's but a 4 plex is whole another animal!

@Greg S.Why would you even consider renewing their lease if they'd treat the property in such a manner and are "animals"?

second @J Scott  thought process here.. completely different animal from rehab.the GC will and is Key to your success. along with how are you going to finance it.. spec loans are not rehab loans.. very small niche and generally not available to first timers..now owner builder move into the home there are plenty of those loan products out there from local banks usually.I think moving into new construction is a progression... myself it was as a lender in possession IE I foreclosed on would be builders who went busto .. and I HAD to finish the projects as I was the money....