even ubers: bring your sniper and heals to the top left building and work picks. once you get a pick, exchange ubers from bottom left with pressure from other players on your team from other entrances. you can also walk in the right building (tiles) or go main (it's easier to get the force from tiles though), and just exchange ubers right away instead of waiting for a pick. the decision to wait for a pick depends on how much time you have left. if you have a lot of time left to push, just wait for a pick. during every trade on this point, you should be getting cap time with your engi, scout, or spy. it's ideal to have your spy, though, sap the gun during the uber exchange (people on your team should make sure they're ready to shoot it when it's capped) so you can repush after ubers are faded. it is payload, so once ubers and the sentry are out of the way, you can keep on dry pushing as a team; you spawn faster (with a tele), so you should take the fight very aggressively into their spawn while getting cap time. there are many more things you can do during even ubers as a "strat" but you most definitely want to abuse the fact that you can keep on repushing to get cap time on this point.
uber ad: this situation will most likely occur when the other team is not setup, so just flood main aggressively to lock them in the spawn while getting cap time. even if they are setup, the same thing works.