Looking for definition of Common Elements

Can you suggest a good source for defining "common elements"? Our bylaws are so arcane as to include patios and balconies but ignore roof access (through skylights in four units for a 3-story building with 13 units) and specify "surface above ceiling." We need common-sense, plain-English language to clarify--especially in a historic building plagued with water issues, in many cases of unidentifiable origin.