Despite the fact that it doesn't have a ton of O gauge rolling stock, Tommy Gilbert's is a great hobby shop. It has lots of scratch building materials, books, and tools. And the staff is very friendly and helpful. Tommy does spectacular custom painting and he transformed my Western Pacific Lionel S-2 Alco switcher into Weirton Steel's #208, complete with stack modifications. It is very sharp and one of my favorite engines.
I highly recommend his shop. It's on Water Street in Gettysburg.
George