I finally built an electric shop for my business last December. I did it then because several positives lined up at the time.
2007 was a very high profit year for me and I could either give it to Uncle Sam or invest it in a building I needed.
My main supply house offered to set up to $30k of materials at my shop on consignment, meaning I only paid for what I drew from the on-site inventory at the end of the month.
Separate service/meter for my building as well as phone line, insurance and gas make it clearly deductible, no red flags.
I put in (2) 10 x 10 OH doors, one with a keypad entry so the supply house delivery guy can have access when I'm not there. Same for my UPS and Fedex guys. It has been great having all of the materials I need at my fingertips every day. Real handy during the ice storm here a few weeks ago. I was able to work all hours until the outages were over.
For 15 years I had an office in my garage and stored tools and some materials in my garage and in a barn. Not too handy. My building is 30x50x12 high. I have a 12x14 heated/cooled office and a 12x16 heated/cooled workshop inside the building. The rest is for the truck and cold storage of materials. It is about 100' from my house so it is close enough to be handy but far enough that my noise/activity doesn't bother the family.