Today I biked into Uni, about 12.5km in drizzle. I wore a Trespass (I think) jacket. My legs got wet, unsurprisingly.
If I had to go in and was really thrashing down (it can be horrible), I'd wear some waterproof trousers as well (dunno the brand). My boots are waterproof enough as-is, but if I'm walking about in mud, I wear wellies, 'cos they're easier to clean.
I've been out in just wellies and waterproof trousers over my non-waterproofs and not got my top half wet. That may have had something to do with the huge umbrella (parasol) I took though
I do get lots of sweat buildup with my gear, the trespass jacket is better than the one that came with the trousers though!