Although I do not advertise this portion of my business, I do govt, mechanical and engineering imagery. All structure based in some way or the other.
I simply use a small level (lwalmart, lowes etc) and place under the body and then on the side. Always on a tripod of course, and then review the image to make sure lines are good depending on what lens I use. I do a lot of this with a wide angle lens and of course fix till my heart is content in PS. Yes, I do stitch images as well depending on the shots. but you can get a tripod head with a level, but that wont necessarily level the body. Remember, the body has to attach to the plate and then the tripod. Use the body.