If it is a wood roof structure I wouldn't hang anything from it unless a registered / certified structural engineer signed-off on it. Steel pinch-plates are inexpensive to have fabricated, and load-rated thru-bolts are relatively inexpensive, too, so the material cost for some permanent hang points is very little compared to the labor costs and insurance claim risk of 'field-engineered' solutions. There are lots of places that are just not designed to have overhead rigging attached to it. Use
ground supported rigging, know the capacity (of both the floor under it
and the trussing). In Japan many smaller theatres were built with a fly
house and no rigging, so every show that comes in builds a
ground supported show rig to sit inside the
stage house. If the promoters don't like the look of the corner support columns, then get them pay for some engineering to get load-rated hang points spaced-out at a workable interval. Of course, you can drape the columns with some fabric, too, to make it look a little better (or use a dark color to make it 'go away').
I think one of the biggest challenges will be getting people to not over-load the new fixed rigging points. Even if a load limit label is attached directly to it, people look at a chunk of steel and think they can hang a car from it with nary a forethought to the material the steel is connected-to. This would be a good time to permanently install a
load cell system so the roof loading points can all be truthfully monitored. It may be that there will be many 500 Lb. pick points in lieu of a few 2,000 Lb. pick points. It is also extremely important to design the anchor points so they can take the lateral loading from bridles. I frequently see giant eye-bolts that don't pivot to align with the direction of loading and then see them side-loaded by the rigging that is attached. You have to clearly define this typical 'not straight down' loading condition to structural engineers because they generally don't understand how show rigging is implemented and assume every load is towards the center of the Earth.
Another thing for the
venue owner to understand is that wood beams can crack and become significantly weaker (read-up about the Oregon Shakespeare Festival
venue when they found the giant wood roof beams there had major cracks). A rigorous annual roof inspection would be a reasonable expectation if the roof is regularly being loaded with show equipment. Spotting cracked wood members early can truly save lives in that kind of
venue.