I know on my washes that the steel ceiling perlins are required for structural integrity of the building. Earth quake codes are the reason. I have seen many washes built with a open end bay that has no roof. Most people who have one say they would never do it again. Lisa Lyons has a wash in So. Cal that has 4 ceiling booms per bay.
I've got an open end bay with only one side wall. I was only allowed to do it if I used a sewer diversion valve. That is a valve that diverts the waste water to sewer when the bay is in use. When turned off and it rains it switches back to storm water after so many gallons of flush (rain) water.
Good thing about it: Cheaper than a building. You can have a "huge" bay for trucks and their trailors, since the only "building" restriction is the slope into your pit. And it is easy for big trucks to go in and out easily. Bad thing: nobody sees the bay or wants to use it since it is in the sun/rain and every 5 months the valve plays up. Thanks but I wouldn't do it again.
On the other hand some years ago I was in Italy and Greece. They have their IBAs out in the open. No building at all...and no walls to clean!