*sorry I started to work on this before the above post was made (please consider the points above too)*
maybe we should get back on topic?
In my eyes, the formation of a mono team isn't inherently different than building a "regular" team. The limitation is only on typing.
Pick the kind of team we want to run. (From the general consensus it seems like balance is best, which I would agree)
So to start we form a balance team and then look for any "common" threats that can run through the team. As many of these threats are identified as possible, and then we try to come up with appropriate checks and counters without changing the overall feel of the team too much. Then comes testing and tweaking.
To summarize what we have thus far...
Politoed (For perma-rain) Bulky set
Swampert or Quagsire (We are leaning towards Quag? with Ice Beam for Dragon DDers?)
Tentacruel (bulky for spinning and t-spikes, maybe strong sp. atk poison move)
Gyarados (offensive DD set with sub and bounce)
Empoleon (sp def bulky, maybe with aqua jet, but otherwise a special set? personal thought - it would be nice to have roar, hp electric or grass knot, ice beam? )
for last slot many things have been thrown around. Starmie, Kingdra, Vaporeon, Ludicolo, even Lapras.
Also personal thought. Shell smash Cloyster (standard set) to attempt the end game sweep after letting Gyarados weaken some stuff.
-let downs of the set above: no reliable healing other than maybe Quagsire, and not using Vaporeon means no wishes (still a very viable option however) Only 1 electric resist, only 2 are neutral to grass. No dedicated status absorber. Poison, Para, and to an extent burn can be played around, but excellent prediction and appropriate switches will make it hard. Sleep is bad news period (can possibly use Poli to take the sleep) And no cleric to clear status.
-good things this set has: Decent amount of offense, perma-rain to counter and probably win weather wars, decent defense with hazards and a spinner, phazer, and respectable dual typing that attempts to cover some weaknesses (going to be hard to get much better than what this has)
Just so we don't lose the progress we've made.