So what sort of level of stats make a particular champion tanky or squishy.

I ask cause i look at the base stats of most champions and they're really pretty similar. yet i know if i go say twitch i last like two hits yet kogmaw i seem to last that bit longer and be a little harder to kill. Yet the difference in stats seem to only be 200ish hp and 3 armour.

so i guess im asking is this as small a difference as it seems? What sort of base stats should i be comparing the different clases at? whats high and low hp for a tank, fighter or carry?

Early game, especially level 1, HP makes a huge different. 180 HP can mean as many as 5 more hits to kill by the support and at least 2 more if not 3 more hits to kill by the ADC.

Generally, squishy champions are often refereed to range champions. They can attack enemy from distance, and so, they usually only build damage on them.

On the other hand, melee champions need to be very close to enemy to do damage. During team fight, they are the most easy one to target. So, they usually build some defense items to increase their survivability. Some even have skills to increase their defense. These champions are often refereed as bruisers or tanks.

As for the difference in stats, I think Devious explains it all

Level 1 sona has less HP than a caster minion. Level 1 GP has over 600 hp with no added bonuses. Its a pretty big deal when each AA is doing roughly 50 at a time

It's a mixture of both base hitpoints and armor/magic resist. Also remember that all three of those stats scale per level at different rates.

Early = HP
Late = Armor