Here's an interesting list. It is the items that each F1 constructor must build themselves. Caterham team principal Cyril Abiteboul believes Formula 1 must consider easing the criteria that teams have to meet in order to qualify as a constructor.
Monocoque
Survival cell as defined in Article 1.14 of the F1 Technical Regulations
Front and side impact structures used to meet the requirements of Articles 16.2, 16.3 and 16.4 of the F1 Technical Regulations
Roll-over structures roll structures as regulated by Article 15.2 of the F1 Technical Regulations
Front and rear suspension without rotating parts
Suspension geometry and suspension members as regulated by Articles 10.2 and 10.3 of the F1 Technical Regulations
Heat exchanges (oil and water)
Bodywork as defined in Article 1.4 of the F1 Technical Regulations and regulated by Article 3 of the F1 Technical Regulations with the exception of airboxes, engine exhausts and any prescribed bodywork geometries
Wings
All parts of the steering system
Seat
The brake and throttle pedal assemblies and mechanisms
Pedals
Brake balance adjustment
Front and rear brake duct
Front wing adjustment actuation system
Switchboard and paddles
Floor
Diffuser
Fuel cell
Some of the things, like the monocoque, survival cell, impact & roll over structures, bodywork, floor, diffuser and wings seem obvious. I'm not so sure about things like steering racks and switchgear. I really don't see the point of insisting that the teams not be able to buy items like the heat exchangers (radiators), seats and fuel cells. Allowing teams to buy such items "off the rack" could save the smaller teams precious time, money and effort in their R&D departments.
http://www.racer.com/caterham-f1-constructor-rules-should-be-eased/article/280520/?DCMP=EMC-RACER_DAILY&spMailingID=5615537&spUserID=MjMyNjk2NjU2MQS2&spJobID=66240771&spReportId=NjYyNDA3NzES1