It starts in champ select. By not selecting them. Both don't really work in the current meta.
But, if you insist.
Swain: RoA or Archangel's for mana issues and core item, in order of preference. Zhonya's, liandry's, voidstaff, spirit visage are all good choices to round it out.
Maokai: tanky as according to team comp. If you can't decide based on that alone, this isn't the right champ for you. Mao functions as a utility tank, so you don't get very much build variation. If you have to cheese it, he does decent ap damage, so a RoA core with deathcap and void can make every bush dangerous.