"a permanent maintenance staff of skilled tradesmen"
= staff = workers made up of "tradesmen" = people who are trained in a trade as a profession e.g., plumber, electrician, carpenter, etc.)
= what kind of 'staff"? = maintenance staff = workers whose job it is to 'maintain' whatever that needs to be maintained e.g., plumbers maintain the pipes in a building, electricians maintain the electrical cords and sockets, etc. in a building, etc.
= a "permanent" maintenance staff = workers who have been hired to work will always have a job at this establishment
Hope this helps a little :)