I've been using a pair of bib type pants for years that are actually made for snow skiing. They are Gore-Tex (or the equivalent breathable/waterproof material), have suspenders, and because they are ski related, have a tougher fabric on the lower inside portion of the pants legs to stop abrasion/wear from ski boots. I've had them for well over 10 years and have worn them skiing, riding, fishing, and camping. Waterproof zippers that go all the way up the outside seam for ease of putting on/taking off. Arc'teryx is the brand. They are not cheap, however. I also have their jacket shell, but it is impractical for a motorcycle due to the hood, so I purchased a HD Pack Lite Gore Tex jacket I found on sale and it has served me well.
Whatever you buy, just make sure it's breathable fabric similar to Gore Tex or you might as well just ride without in hot weather, 'cause you'll sweat so much you'll get wet from the inside out. Coated fabric is like being in a Sauna.