Shane,
If you have the room take the ceiling to 16', that way you can build a loft giving you 7.5' of ceiling above and below. The lower level can be the tool room, wood/metal shop and above can be extra storage or a trophy room/man cave (that's what I did in mine...it's 15 x 30).
My main door into the shop is 20' wide and 12' tall which makes it easy to drive in.
The only mistake I made was not installing a toilet. I have water, heat and a washing machine. While I had the trench open to bring water from the house to the shop I ran a 1/2" copper line to back feed compressed air to the garage at the house. That way when the wife wants to blow up a pool float for the kids she have it handy.
Looking forward to seeing pictures of the new shop and the project truck...I know they will both be great!
Mike B
