After rain it won't fjre
Clearly something is getting wet, when the check engine light goes on take the car to autozone or advance auto and let them scan the car for codes for free...
You will probably find that moisture is getting into your distributor cap from rainwater entering through a break in the hood seal. It is along the rear edge of the hood edge or where it meets the fire wall. The Distributor cap is near the center at the rear of the engine (if it is a rear wheel drive car).
Also check your spark plug wires. Those too when they get old break down electrically and will cause the engine to misfire/not start when wet.
Looking for a Used Roadmaster in your area?
CarGurus has 68 nationwide Roadmaster listings and the tools to find you a great deal.
Search Buick Roadmaster Questions
Buick Roadmaster Experts