When should I paint the major parts of a model?

Build the kit in several sub-assemblies. Build wings, fuselage, any weapons stores, and cockpit, then you can paint the sub-assemblies before putting the entire model together. Kit directions usually have you start with one piece and glue all parts around that piece until you have an entire aircraft. This is just not very practical. Building and painting in sub assemblies is the way to go.

I used to prepaint almost all of my models, at least to some degree, but I've found that airbrushing them when they're assembled gives a more realistic appearance. I WILL leave off the props, landing gear, exaust and anything else that could easily be added afterwards that would be difficult to mask. The cockpit is entirely painted and weathered and then sealed with the canopy that has been masked with Bare Metal Foil prior to the finish coat. But that's just me.

If you prepaint a wing and fuselage and the joints need to be filled, you'll most likely wreck your paintjob and have to repair it later. Not to mention getting oils and fingerprints on the model.

The best way to build/paint a model is to do it in a way that you enjoy and feel comfortable with.

-fish

I would agree about sub-assemblies being painted seperated from the actual aircraft, but when it comes to painting the aircraft itself you wait until the wings, and horizontal stabilizers are all glued to the fuselage and then paint the entire fuselage and wings as one unit. Then you can glue your sub assemblies on such as landing gear, weapons, prop, etc.
Just remember to stuff some paper towel material or kleenex material down into the cockpit area to protect it from overspray when painting the fuselage.

Mike