Personally, I wouldn't build one for my first AR, particularly from parts you piece together (buying a complete un-assembled kit would be different). Get familiar with the weapon first, then build something. Only then will you know what parts you want in your build. Putting together a rifle you aren't familiar with with seconds parts sounds a recipe for disaster to me.
Besides, you really won't gain much in building something for roughly $600 that a brand new sport will cost.

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686/M&P9 Pro/M&P15X/M&P15-22