Most of your army should be made up of stuff designated as necron. Start with warriors, destroyers and wraiths, I wouldn't start getting pariahs and flayed ones till later once you have a decent size army.
Flayed Ones are Necrons. One of the most downright vile armies I've played against was a Necron Assault army that had a pair of lords on foot, three ten-man squads of Flayed Ones, two twelve-strong units of Warriors, and a pair of units of Destroyers, each three-strong.
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