The smartest birds use claws and beaks to manipulate tools and stuff pretty effectively. Hummingbirds as we know them can do neither - their feet are extremely limited (compared to, say, a parrot's) and their weak flimsy beaks barely articulate since they only really need to stick their tongues out to eat from flowers or weave tiny fibers into a nest (compared to, say, a raven's). Their wings have developed to perfectly suit their size and mobility needs, so those probably need to remain unchanged. And their extremely tiny brains cannot hold a complex enough network of neurons to be capable of intelligence comparable to humans. If you make it any larger, then their already extreme dietary needs (they must eat pretty much constantly) would grow too great for their little bodies to sustain.
There's just not a realistic way to explain a hummingbird with the abilities you describe. You'd have to change their physiology substantially, to the point where they don't resemble hummingbirds at all. If you want a story about intelligent inventive hummingbirds then you're better off just giving them hands and handwaving their intelligence.