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As per your request, I would start out with a real one and take away all the unnecessary parts and shrink it all down. If you don't need it to fly, start with a big piece of wood and carve away anything that does not look like a helicupter.
Other than that you would need a motor, a frame. a control box to control the servos for the flight mechanism, senders and receivers for the remote box. whether you want 2 blades or 1 to hover and steer. (additional servos may be required) A nice company to prepare plastic parts for construction of helicupter. And oh yeah light weight batteries.
Thats just a start off the top of my head. Might be cheaper to just buy one. There are kits available with remote and without. (cable guided).
You really should check on line and study the apparatus required to build and control said helicupter. It's not exactly a weekend project even if you purchase a kit.
Good luck with whatever you choose! If you do attempt it, please keep us informed of your progress!
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