The goal of custom Lego sets? To try and shape together what important pieces of the Star Wars saga that to date have either been overlooked by TLG... or will never be properly produced.
My "work" mostly focuses on Cloud City. Although nearly half of ESB takes place there (including critical scenes such as the "I am your father" duel and Han being frozen in carbonite), TLG produced only one kit (10123) and the now greatly inflated price and clumsy design didn't appeal to me. The newest build of Cloud City is my third, and tries to take design cues from the Death Star by having a notional outer shape with many exposed playsets within.
I've also got a custom sandcrawler, Mos Eisley + cantina, Yavin 4 rebel base and a smaller take on Grevious' flagship, The Invisible Hand.