This is my team building process... it may be unorthodox or it might not even work, but it is what it is :)
First of all, I have a copy/paste of Orch's threat list out and ready to use... it's extremely important to have said Mons checked, or it's very potential to have immense problems with them <cb ho-oh with no rocks up>. That being said, it remains important to still have some form of SR. In my opinion, the best stealth rock setters remain Deoxys D/S, Dialga, Groudon, Ferrothorn and (possibly) blobs. Out of those options, I'd typically go with Groudon, but choose whatever fits your team right. A stealth rock setter is one of the last things I'd add to my team.
One of the most important things about team building (imho) is that you absolutely require a core. (If you don't know, a core is 2-3 Pokèmon that synergize extremely well together.) Typically, I go with either powerhouses in Ubers, or start off with one Mon that I really like, and build the rest of the core around it. Just for example here, let's say we took CB Ho-Oh. CB Ho-Oh is weak mainly to 3 things; Stealth Rocks, Groudon and Rockceus. Whilst there may be more and arguably better counters, those are without a doubt the most prominent ones. Since Ho-Oh is undeniably weak to all 3 of the aforementioned things, this will be a 3-teammate-core. First of all, we need a defogger; Ho-Oh absolutely requires Defog support. Typically, people will go with an Arceus-forme this gen, and it's a tried and true method. I like to run an Arceus form specially defensive with 248 in HP, 252 in SDef and 8 in SpA, with a Calm nature, but it's personal preference as to whether you want it physically tanky or specially tanky.
So, now, we have Ho-Oh and an Arceus form (let's go with Grass, shall we?). Arceus-Grass is an extremely reliable check to all of the three main Ho-Oh checks. So now; what is Arceus-Grass weak to? Fire, flying.... does that sound familiar? Even though you have a defogger, it's still almost mandatory to have a check to Ho-Oh in the form of Stealth Rocks, thereby requiring an SR user. Since I'm running specially defensive Arceus, I'd like a physically tanky SR setter... sound familiar? In adding Groudon to the team, I now have a reliable E-Killer check, and I have Stealth Rocks AND a check to Ho-Oh formes.
Ho-Oh, Grassceus and Groudon; 2/3 of them are extremely weak to a certain water behemoth... Kyogre has been the champion of Ubers ever since its fateful release in Gen 3, and it is absolutely mandatory to have a check to it. What's the best check to Kyogre, you ask?
And I quote Donkey; "fucking palkia weak"
Since my team thus far would appreciate special damage, and a check to Kyogre, SpecsKia seems like a good addition to this team, does it not? SpecsKia is a set not many people expect, and it is capable of both taming the ogre and dishing out some huge damage.
Ho-Oh, Grassceus, Groudon, Palkia... What's that weak to? Or, better yet; what's something that it DOESN'T check? O deer god.... (ba dum tsp)
Xerneas is a MONSTER. With absolutely no support required from its team, it's an extremely versatile, unpredictable Mon that can absolutely rip teams apart. The best counter to Xerneas, in my opinion, is Aegislash.... however, Aegislash doesn't do much effectively outside of being a Xerneas counter. So, I decided to add Jirachi to my team. Apart from the extremely rare HP Fire, Xerneas can't do !@#% to Jirachi. I'd run TWave and Iron Head to maximize Xerneas-shut-down-ness. ;)
Ho-Oh, Grassceus, Groudon, Palkia, Jirachi... I'd argue that this team is fairly even right now. That being said, it needs one more addition. Whenever I'm in a situation like this, I break it down to typings.
Fire, Flying, Grass, Ground, Water, Dragon, Steel, Psychic. Those typings are rather prone to Scarfkrom, Darkrai and Mega-Gengar... what beats all three? Priority. And while the last slot is PURELY personal preference on what you think you need checks on, I decided to add Mega-Kangaskhan to this team. Fake Out and Sucker Punch give it the ability to save your team from so many threats, and with an incredible ability before and after mega-evolution to boot. If you don't mega evolve it, you can use Scrappy to it's full most potential by faking out the Mega-Gengar, and proceeding to mega evolve and use Sucker Punch. This beats pure speed sweepers, breaks focus sashes and rounds out the team nicely.
So, in that, my example team is:
Ho-Oh, Arceus-Grass, Groudon, Jirachi, Palkia and Kangaskhan.
While your team may end up looking like something not even close to that, I truly believe the process to getting that team works quite well.
Please let me know how this works, and your opinions on it; all feedback is appreciated. ;] oh my god I almost used edgrr's smiley face