I dunno - it might take some outside-the-box thinking. Large-scale structures like buildings, yeah they'll just fall apart into hills of indiscriminate rubble and rust away to formlessness eventually; but what about smaller things - say, metal hand tools? When these fall on the ground they tend to wind up covered and buried quickly, and that is very important: under the ground, the metal will still rust away but it will leave a mold, which can fill and essentially fossilize. And fossils can last a heck of a long time.
Wood also likes to last a long time and can fossilize. Human-worked wood will fossilize into shapes that will be recognizable as worked; in fact, whole wood structures might end up being preserved - rising sea levels will eventually inundate cities and the wooden frames of buildings will end up preserved in much the same way as submerged forests,
which can last for tens of thousands of years or longer. Wood that petrifies can last way longer - there's petrified forests in Newfoundland that are over 300 million years old.
But I think the far longest to last will be trace fossils. These are your famous dinosaur footprints and things made in that way: animals making imprints in the surface that get filled in and preserved as layers deposit on top. We have trace burrows from simple tiny critters that are over
2 billion years old. These:
...are called climactichnites; they're the fossilized tracks of gigantic ten-foot-long Cambrian worms that lived 500 million years ago, made as they slithered along over the mud. In time the mud in that location became stone, and the tracks are now preserved for a good long time. If it occurs to you that they kinda sorta look a little like tire tracks (but wigglier), that's what I'm getting at. Humans are bound to leave behind some shoe prints, boot prints, and tire and tread tracks that should be pretty unmistakeably technological to a scientific civilization examining them in 500 million years; that Nike Swoosh is not likely to be mistaken for the actual shape of a critter's foot-pad.