Are there specific mass breakdowns for aircraft? I am interested in the engineering and weights for aircraft around 8,059 lb (3,655 kg) Citation 505) and  18,900 lb (8,570 kg F-16).

Curious about specifically structural mass and landing gear systems. How much can landing gears lift?
I can point you at some reference materials you can use. These methods involve estimates for different types of aircraft and formulas you can use to estimate the component weight based on the MTOW and OEW, for example.

You can use the following books:


Roskam - Airplane design (a series of books)
Egbert Torenbeek - Synthesis of Subsonic Airplane Design
Jane's All the World's Aircraft (over 600 aircraft)


scholar.google.com is another good source for finding articles about landing gear systems and design in general.