Doing it at home is possible, but the hard part is the colour match, not the spraying. Original Monza blue fades differently from panel to panel, so a fresh mix might look spot on on the rear and roof but clash with the factory wings and doors in the sun. Get the paint code off the door shut plate, take it to a decent paint supplier, and ask them to make up a test card. Then compare it against the bonnet or a sheltered bit of the wing before you commit. If the roof and rear are a mess, sanding them back properly is most of the job, and that's where a cheap home attempt usually goes wrong. You might get a better result for the money by paying an independent body shop to do just those panels and blend the wings, rather than a full respray.
