Everyone will have different thoughts on this but in this case I think your wife is right. Put the woodworking in the shed and leave the cars in the garage. The cars are heavy and not many sheds really have strong enough floors long term.

When you do run electric to the shed, run way more than you think you will need. At least 100amp.

Good luck with your endeavors.

 

As long as the ceiling is 8' or more it should be doable. You don't say what you have in terms of workflow, but you should be able to put the usual tools in that space. Since you do woodwork, you are likely accustomed to drawing plans. Draw one for the new space and see if your tools will fit as you like. Finally, if you are in a humid locale, then I would not put tools in the space until it has climate control.

Interesting that you joined this site in 2014, yet this is your sixth post!

 

The ceiling height is comparable to the area I'm in now. I have not drawn out a plan yet due to we are getting the building anyway. I just wanted some feedback from someone in a similar environment. LOL about the six posts, I kind of took a break from woodworking. I got burned out on it some years back as it was part of my day job. I'm starting to get back into it. My work flow now is smaller items and furniture. Nothing on a production basis.

 

Based on location, a metal building gets pretty hot in the summer (120 degrees) and pretty cold in the winter. I am in Texas but had similar issues in North Carolina. That is something you will have to compensate or just do seasonal work in the shop. An adjoined covered space with open walls may help if you have your tools on wheels/dollies and make a study outdoor bench under the awning. Just my two cents but its how I typically work in my space.

 

Not sure about the climate there, but a detached building would be nice to work out of, it will keep the noise down,and the dust out of the house. Just saying.

 

My workshop is a 14' x 24' portable building. I like it. Seems nice enough for a hobby workshop. Most of the bigger tools are on casters. The ceiling height is 8' but so far not a problem for what I have been doing in there.
Some pictures here: BlasterStumps's Workshop
I insulated it, then drywalled. I also put some plank flooring in. When I first looked into how I wanted to do the interior, I drew the building up on Home Design software. Here is a screenshot of when I was trying to figure out the cabinets, lighting and some tool placement. I have since moved tools and added some workbenches and tool storage that I wasn't able to put on the drawing.

 

Good looking shop BlasterStumps

 

I think working on cars in a 12" shed would not leave much room to move around the perimeter. Plus if you are going to put this on skids, there would be substantial settling and issues with doors, etc. At a minimum I would pour a pad.

There are many folks around doing woodworking in a structure that size on this site, and doing it well. I belong to the penturners site and I think it is quite common over there. I have a shop for auto and mower repair in my garage and a wood shop 90' away. It requires a lot of duplication of tools, but I did not want my woodworking space corrupted by coming and going when I want to do finishing, and likewise I did not want to have to walk up to the woodshop which 130' from the house for a screwdriver or a drill....so I have two shops...it hasn't been cheap, a lot of duplication, but I love it. The wood shop is 1000 sq ft and my wife being a landscaper/flower person did not want it next to the garage which is also a 1000 sq ft. and next to the house. So I compromised....I did everything she wanted! LOL

 

I have a 16' x 27' shop, which was stick build on site. I poured footers and columns then used 6x6 pressure treated beams. Then built from there. I did finish the interior with insulation and sheet rock after running all of the electrical. It has been nice to work in and not having a concrete floor is more comfortable on the feet.