Thanks for the shoutout @Troy Sheets .
Zoning changes include the requirement of a 5' setback for pilot houses at the rear of a property in addition to the 10' at the front of the building. This can make placement very tricky without getting a zoning variance.
Lot coverage is 75% for mid-block properties (for zones that use lot-coverage). The rear-yard setback for lots less than 50' in depth used to be 5' for the first floor and then the greater of 9' or 20% of lot depth. This has recently changed and is now 7' all the way up (but you still have maximum lot coverage to account for).
Of course, a lot of this varies from one zone to the other. Having a good architect on your team will help immensely in knowing how to maximize a lot.
Another huge thing coming up is Philadelphia is about to switch from the 2009 IBC to the 2018 IBC and 2015 IRC (we're in a dual-code overlap for another couple months).
In the 2009 code, if you were able to meet your maximum travel distance, you could have a roof deck (4th floor) that exited out the 3rd floor of the unit it served and get away with a single means of egress. In the 2018 code, if any part of the 4th floor is occupiable (roof decks), then you'll need two means of egress all the way out of the building from that floor (or from the floor the unit exits). This will wreak havoc on tried-and-true plans people have been using.
Also, the Streets Department has been cracking down on front bays if there are utility poles on that side of the street. You have to get permission from the utility company to project a bay into the sidewalk if you're within 10' of a utility line. Since most sidewalks aren't more than 10' wide, this will be more difficult to do moving forward.
All corner lots need Checklist #2 from the Streets Department. I've been handing this off to an engineer to do. It often takes 3+ months to get approval from the streets department. You can still get zoning approval in this time, so plan your schedule accordingly and get it early if you're building on a corner lot. A good Project Manager will be using the critical path method and will have Checklist #2 on it early since it can hold up an entire project.
The Water Department also wants to pre-approve your plans before they approve them. This is done via email and tends to take 1-3 weeks.
That's all I can think of for now. If anyone has questions, feel free to reach out.