Hey, congrats! I was a CHOP Extern last summer and was also coming from outside Philly. I ended up finding a summer sublet on Facebook from the page "Philadelphia - Housing, Apartments, Rooms, Sublets, Roommates." It worked out really well! I recommend trying to get something walking distance to the hospital, I was living near 40th and Chestnut and it was totally walkable. You can also let the Extern Coordinator know that you need housing and she can help you out with living in the UPenn dorms if that is what you prefer. Good luck and have fun!