If I happen to make big money, I'll give you half of it.
Literal
By-chance, I [subject-が] big-money [object-を] earned-[conditional-たら], you [to-に] that's half [object-を] will-give [volitional-あげよう].
大金 ('big money, a large sum') is a compact Sino-Japanese compound. 稼ぐ ('to earn [money]') is the everyday verb for making money. あげよう is the volitional of あげる ('to give out-of-group'), matching the speaker→listener direction.