The proposed solution "Péter kint lát egy épületet." has an unnatural word order. It should be "Péter egy épületet lát kint.". Also acceptable, but it implies, the emphasis is on Péter being outside: "Péter kint egy épületet lát."
Nope, it does not have an unnatural word order - unlike your example, "Péter kint egy épületet lát" does sound unnatural. "Péter kint" as "Peter outside" sounds like an (intelligible) anglicism to me, it's more natural for "kint" to belong to the verb and not to the noun.