This is the garage we ended up building if you can.It holds my 1975 trcuk,my 17' boat and my 1965 truck.I also has room for my tools,a work bench and a fridge full of beverages.It uses mostly nominal dimensions,has no posts in the middle but does require some engineered trusses for the roof.I only wish I had gone bigger.
https://www.behmdesign.com/garageplans/1080-1.html
Here is a pic.