I came up with an idea for which a device has already been patented which has some of these really broad claims. My design would be very different from the design in the patent, but at the end they both perform the same activity. Also note that the above claim is a dependent claim.
Read each claim. If you avoid even one step in a claim, then you don’t infringe on that claim. If this is true for all the claims then you don’t infringe on the patent. I’m sure there is no claim which is just “The top is made of plastic”. That must be just a part of a longer claim or a dependent claim. This said, it is a really good idea to get an actual patent attorney to give you a freedom to operate opinion.