Any tips on approaching the ADHD spouse about their clutter?

I seriously feel like I am suffocating in this house. I am so tired of trying to pick up and keep things organized, just to have it all blown to pieces by my ADHD husband. I am nothing close to a neat freak, but his piles and projects are killing me. If it was just in his office, I could sigh and close the door. But it is seeping out of his office. The garage is a nightmare thanks to his "Hey how about I spontaneously start tearing down all of the drywall (including the ceiling) so I can insulate and put up new wood" right before Christmas and his busy tax season. The kids can't even get to their outside toys. 

He took over a leadership role in our Cub Scout Pack. (I, of course, warned him it would be a lot of work. He, of course, said, "Oh, it will be fine." ) Anyway, the issue is that he has spread piles of Cub Scout stuff over our entire 8-seat, super nice and new, the focal point of our downstairs, table. 

My son just turned 8 and I said we were not having a big birthday party because of the mess. I do all of the work planning and prepping while he works on a project (ironically, cleaning out the garage for my daughter's party in November. I parked in it for one week before he started the next thing. ) It stresses me out to no end (getting things ready while DH is doing whatever he wants to get ready), so I have to find some kind of alternative plan (inexpensive, of course, since DH just lost his job) for my son.

Because I never know what can set him off, I am trying to find a gentle way to discuss him cleaning it up. So, if any of you have tips on this, please let me know. I have kept everything bottled up for so long that I have no idea how to express things.