A hot-tempered roofer and his baked teenage apprentice climb the ladder of the trade world and swindle their way to success.

Agreed with the above.

Also, is there a way to make this pair more empathetic? That's not to say that the main characters have to be "good" people, but being hot-tempered, stoned, and evidently greedy, aren't qualities that alone give an audience much to hang their hat on. Could they at least have a noble cause motivating them?

In the case of this logline, I think you need to add a bad guy, or something that is standing in the lead character's way.

Also, you are describing "Life as normal" for these characters. A story usually begins when something interrupts the Norm.

As mikepedley85.

And what's so funny about swindling innocent people?

This isn't really a logline. Check out the formula page for more guidance on this.

What's special about the particular period we're following these two? Why now? Why is this different to their "normal" life?

What the inciting incident that kicks this whole story off? What are these two trying to achieve? These are fundamentals of a logline.

How are they swindling people? Are they doing it for the greater good - conventional heroes? Or are they anti-heroes?