Sheet Metal enclosure
I am in the process of designing a sheet metal enclosure,it shall have stand offs to mount the PCB assembly,kindly advise as how much veration in height (standoffs) PCB assembly can afford.
It depends on the size and thickness of the pcb, but generally you'll find that off the shelf standoffs themselves won't vary enough to matter. The data sheet of the pcba material, or general industry rules-of-thumb regarding the expected flatness of a pcba of a given size will usually be far greater than the height variation of off-the-shelf standoffs or formed sheet metal tabs.
I would find out what to expect for the pcb out-of-flatness and then make sure the design was better, or worst case, no worse than the anticipated out-of-flatness for the pcb.