I haven't built filing cabinets from the ground up, but I have modified some. A serious consideration when you design them is to incorporate a way to secure them to the wall if possible. In my case I had to modify both a double wide unit and a tall single wide unit so that they wouldn't tip over if multiple drawers were opened. Both units were heavy and built with oak and oak ply. A user inadvertently left the bottom drawer open on the double wide cabinet and opened the upper drawer. Since both drawers were fully loaded, the file cabinet tipped forward spilling a printer and miscellaneous office things. Fortunately no one got hurt but I quickly added a reinforcement brace to the rear cabinet wall and a spacer between the wall and cabinet since I couldn't attach it directly due to base molding behind the cabinet.
I realize this doesn't directly answer your question, but offer the suggestion for safety consideration. Earthquake restraints could also help, but in my case they weren't aesthetically feasible.