Did a 30 x 40 x 12 Mueller. This is one of their standard buildings. The basic design has one 10' x 10' rollup door. I added a 36" entry door and a second 8' x 8' rollup door. I have the 10' door on the west side 30" and the 8' on the south side 40'. In the summer being able to open both doors and get some ventilation is great. I used Mueller's optional insulation and it really helps keep the building cooler. I had the slab done at 6" thickness for a 2 post lift.
Between a couple of friends and my wife who was a trooper thru the build I got is up in about 3 months of evenings and weekends.
The insulation was a PITA but worth it.
Building from Mueller was about $12K 5 years ago, the concrete included 2 other slabs so if I were to break it out it was about $16K.
Still have to get electric finished, got a freebie 3 tom heat pump for cooling and heat. Yet to install.
I have my building split up into general areas, storage with 2 large home made shelves that are 8' tall (I have some rolling stairs), place to keep the lawn equipment, metal working area with a lathe and vertical mill. General work area where I can park a car when not in use. A place where I can restore my VW Type 3. I have as much stuff on wheels as I can, so I'm not locked into keeping stuff in one place.
I'm near Jarrell, TX.