Unless you have the tools I wouldn't build an upper. And honestly you can't do much better pricewise than the linked $280 uppers from PSA. The quality is there, too. You will have to add their $140 BCG and $15 charging handle which comes to $435. (All this is in stock at the moment but I wouldn't wait too long.) And a rear sight, but you'd need that for an upper build too.
http://palmettostatearmory.com/index...sc&order=price
http://palmettostatearmory.com/index...ier-group.html
http://palmettostatearmory.com/index...ndle-6211.html