10'x 60'

I was gonna say 2 feet wider, 4 feet higher and at least 10 feet longer. you can always stash a few engines there till you get a bigger boat.

For reference, my 32 AT is just over 38' on the steel trailer. My garage is 39.5' deep. If I had an aluminum trailer, it would be longer and probably not fit.
My garage door is 9' tall and it clears easily. It might fit under an 8' tall, but it would be real close.

10' high by 10' wide door covers all, especially if you are old and can't turn your neck to see the right corner!

Thanks everyone for your thoughts. Going to contact my architect and see if I can get to at least 9'. I will have the 4 post lift next to the boat bay to help pull motors if I need to. My budget will likely limit me to a 32' boat for a while. Eventually I'll build a rv/boat specific garage but for now I'd like to stop paying storage and have easy access to work on it at home. Happy boating!

Check your local building codes about the floor drain. our local codes do not permit floor drains in garage bays. Has to do with introducing fuel / oil into storm drains.

As for the door....as big as possible!

You will loose almost 3" with finish trim on all sides of the doors and the floor drains will never work in MA, just had to go with a good pitch on the floor. You want to make them look well with the building and you will always wish you went bigger. I am just finishing this 42x62 barn with 12' doors and wish they were bigger.

Another work around option is put in a sunken drain and then put a few inches of concrete over the “drain”. After all is completed and you get your CO, it is easy to...you get the idea.

Just my .02. ALWAYS go as big as possible and feasible. My Scarab III is 42' coupler to prop. 10 X 10 door mandatory. I did a 30 X 60 garage 12 yrs. ago. Wish I had gone 10' longer. If you can go big now, you will never regret it later. Good luck.

16' wide X 10' tall on the door at minimal if you ask me.