I am repainting the bumpers, hood, and roof on my car and I am using color matched paint to do so. I have noticed that spray paint is a lot cheaper than paint for a spray gun. Would it make sense to spray the base coat with the spray paint then for the use my spray gun for the clear coat or is that a stupid idea?

I will say that it is a bad idea. Mixing two different kinds of paint is asking for trouble.

Alright, thank you. Another question, how much area can I cover with one quart of paint using a spray gun?

You should read a lot more on here and you will learn a lot. Way too many variables to answer that question.

Not trying to ignore the question, but there is not enough info to answer. Maybe someone else can help.

Usually, spray cans come out more expensive in the long run
when doing more than just a little spot, like a bumper.
They don't go very far.
You can buy just a half pint of base, and there are off-brand alternatives
that are much cheaper than the name brands.
And remember, it's reduced to make 1 pint sprayable.
A half pint will usually do most medium to small size bumpers.

From the place I am buying the paint from has ready to spray paint. Would a quart be enough to cover just the roof? It is a 1994 Toyota Corolla Wagon.