Among other things, I’m a re-seller of pre-engineered buildings.
By the time you get a metal stick building delivered and assembled on site, you can usually figure to tie up about $45 to $50/SF or so.
You can install an attractive façade on the front and sides for another $10 to $15/SF or so.
Throw in another $15,000 or so for tongue-in-groove paneling on ceiling and sidewalls.
By the time you get done, the cost would approach that of a glass building.
For liability purposes, I would consider a set of inexpensive roll-up access
doors in the event you need to shut the wash down for some purpose.
Glass side walls and windows may be a hassle to keep clean sometimes but I can assure you customers prefer washes with the wide-open feel to them.
How much better does it get when motorists can see other people having their cars cleaned or the picture it can create at night?
For less than a couple of grand, you can build your own window rinse system out of PVC using the same approach as a lawn irrigation system.