Roaming and backdooring is a viable strategy in Dominion. They are situational tactics that aren’t useful if you constantly apply them and forget to defend your points. However, used at the right moment they can help solidify your lead or help in a comeback.
When you plan to roam the first purchase should be Boots of Swiftness or Boots of Mobility. Both are good items: the former’s bonus is constant, the latter’s is temporary but higher. If your champion’s base movement speed (MS) plus the boots’ bonus MS is at least 400 buy Boots of Swiftness (bonus MS: 90), if it’s less buy Boots of Mobility (bonus MS: 130/70).