i think the big problem you're going to face is that due to the laws of physics and engineering, lightweight, waterproof and 'summer' don't fit in the same box.
in order to be waterproof a walking boot needs to be fitted with some form or other of plastic bag to go around your feet - not only does this make the 'summer' bit rather difficult, but that plastic bag is extremely delicate and so has to be protected on both sides by lots of material. this is not condusive to 'lightweight'...
go for a leather boot that does not have a lining (gore-tex, Sympa-tex, sweat-like-a-pig-tex, tesco-tex..). if you want something higher than the normal walking boot to cope with brush and vegetation the best you'll find on the market is the Alt-berg Defender: its entirely comfortable to wear all day even in very wet conditions, its pretty robust, you'll get them for about £40 - £50 on ebay, and unlike a lined boot its easy and quick to dry.