In most cases if you want a switchboard or even a larger panelboard (like I-line or similar) you get much better pricing if you order complete with branch/feeder devices rather than adding them separately after the fact. If not knowing what branch/feeders should be installed in it, might as well just put in a 800 amp fused disconnect or 800 amp breaker in individual enclosure and call it done. Let the other contractor connect whatever is needed from there.
I could see it being possible that you maybe are asked to install 800 amp service conductors and maybe a main with a determined number of say 150 or 200 amp feeder breakers and the other contractor does everything beyond that.
Another possibility depending on what you are obligated to provide is you maybe install items from utility pole/transformer to a CT cabinet and the other contractor runs everything else from there.