In reply to NinoFabio:
It's certainly not tailored. If you lay most waterproofs out flat with the zip done up, they're straight from armpit to hem. Take a 73kg, 6ft climber with a 32 inch waist who would wear a 38 Long suit. Then put him in a large waterproof - it fits like a sack, but the hem and the tops and ends of the sleeves are in the right places. If he puts the hood up, the jacket doesn't lift his arms up either.
If he puts on a baselayer and a couple of thin fleeces and and a thick softshell and a belay jacket, then he looks like a barrel but can still move his arms fairly normally (and can climb still the last few pitches like that if the weather has totally crapped out).
If you put him in a medium waterproof, his arms dangle out of the end of the sleeves and he can't raise his arms above his head without the whole thing riding up. If he tries to wear it over a belay jacket, he looks like an over-stuffed turkey with as much freedom of movement. If he puts the hood up, his arms may now point at the horizon.
The waist's not a concern - it's always the shoulders and arm length. There's always lots of spare fabric around the waist if I'm not wearing lots of layers. Now if I hung a 42 inch waist around my frame it would be a different story, but then maybe I wouldn't need a belay jacket.