smogon is down!!! i dont have any idea what kind of team to build with out some kind of instruction.
THIS IS NICOLE NOT ANDREW!
IMO...
You'll probably want a water type. Suicune, Starmie, Gyarados, or Swampert. It depends what you want your water type to do (starmie and gyarados are good at attacking, swampert and suicune are better at tanking). Water types are one of the better types thanks to only three types resisting it and water pokemons' ability to learn an ice move (an ice move is INCREDIBLY NECESSARY FOR EVERY TEAM, make sure you have one!) Almost every team has a water type.
You already said you wanted Tyranitar, he's good, so I wont say anything about him.
You want at least one special sweeper and one physical sweeper. Sweepers are both fast and strong, but cannot live long and shouldn't be expected to. You might consider a mixed sweeper also, but I don't really care for those. Gengar is an excellent special sweeper - you want to get something to sweep for you with a similar spread of stats. Tyranitar is a physical sweeper already. Infernape or Lucario are both excellent mixed sweepers, if you want one of those.
You need a special wall and a physical wall, and possibly a staller as well. A special wall is something like blissey, with ******** sp. defense and ******** hp, but not much else. A physical wall would be something like Forretress, with multiple resistances and high pysical defense. A staller is something like Dusknoir or Bronzong - these pokemon can support the rest of your team by setting things up (stealth rock, for example, hurts every pokemon the opponent brings in once it's set up, and can only be removed by a move called rapid spin, which only a few pokemon learn) and are very annoying to kill (though they are usually very weak attackers). Some pokemon, such as Ninjask, can learn baton pass, which passes stat boosts to another pokemon. This means if you use moves that boost your speed stat and then pass that on, you can use a slow, stroing pokemon to sweep when you otherwise couldn't.
The two teams I've made thus far, to give you some ideas:
Gengar (sp. sweep), Bronzong (stall), Weezing (p. wall), Gyarados (p. sweep), Marowak (p. sweep), Snorlax (sp. wall). [don't use marowak]
Infernape (mix sweep), Blissey (sp. wall), Skarmory (p. wall), Weavile (p. sweep), Alakazam (sp. sweep), Dusknoir (stall).
Try not to have more than one of the same type. Try also to have types that can cover each others' weaknesses and ineffectiveness. Try also to have sweepers that can either learn a wide variety of moves or a couple moves that nothing can resist (the combination of electric + ice is not resistable by any pokemon...if you have a pokemon with an electric move and an ice move, it will always do at least neutral damage to your opponent). The pokemon all get STAB. I'll use fire types as an example, though it applys to all types. A fire pokemon using a fire move will hit with 1.5x more power than normal. Keep this in mind when choosing moves and your pokemon, and what moves to teach them.
Items you give your pokemon are super important as well. You want one of your sweepers to have a life orb for sure - this will make their moves 30% stronger while taking away a bit of health each time they use an attack. Considering that sweepers aren't supposed to get hit, like, ever, because they'll usually die in one or two hits, it's ok that they lose some health. I can't really tell you anything else specific about items, because they're VERY specific to each pokemon and what you're using that pokemon for. You'd have to post what pokemon you were wanting to use.
Sorry for this long post, I hope you didn't know most of that stuff already!
OK IM ANDREW AGAIN.