Mine is 40x30 with a 10ft. door. The first couples times it was kind of scary but now that I am use to it and it's all good. I do have some markers along the way to make sure I am on track backing in. If I had to do it over i would go with a 12 ft. door.

Getting close a 48x60 with one 18 x14 door and one 12x10 door

I agree - a 12' wide door. As several as said above, build as big as you can. It's never big enough. One thing that hasn't been mentioned is windows. If this is at a weekend place, I suggest having no windows. It allows for a very easy and quick way in for a thief. I realize you can still get into a shop with no windows as well, but it takes a lot more effort.

I also suggest going with a slide up garage door rather than a roll up door. The garage door seals better. I have roll up doors, and I'm constantly fighting dust and a few random leaves.

Really depends on available funds, if you have 35k sitting around then the sky is the limit really for a 21 foot boat. I went with an 18x30 for my 21 foot Skeeter and there is plenty of room. 12x12 roll up door, 5 windows, and standard walk in door. Its perfect. Slab and all was under 14k. Texas Choice Steel Buildings was who i used, they were fairly easy to work with. The city on the other hand was not.

I'm going 30'x40' with a 16' door.

From someone who built houses for a long time: an 18’ door is only a few bucks more and it makes a “barely two vehicle garage” into an “easy two vehicle garage”. That extra 2’ is huge.