We work with a lot of investors who have done new construction in Philadelphia. Some of our clients are currently building right now. We also have several lots on the market - would recommend you check out our site and browse around at http://www.thesomersteam.com .
As far as a shell vs lot, it depends. Some of the shells are so bad or might not have the layout you are looking for so the shell may need to be demolished which would add to your cost. If you find a shell that you can use it does save some time unless you want to do new construction - that would be a personal preference.
You can speak to several contractors or go to the philadelphia website as far as the process - it can be very complicated to not too bad if no variances are required. It does typically always take longer than planned though. If you need additional info, go to our website and shoot me an email via the contact page.
Good luck !
It all depends on how much money do you have. Can you pay the lot all cash? and only carry the construction. If the money is not a issue, you can do any orders. If you do need borrow money to buy lot and build.You need check with the lenders. The lender will charge higher interest for an empty lot vs the lot with a small house.
Do plan before you buy it.