Making drop control arms

What actually makes its a drop control arm. Is it in the deminsions or is it just the cup placement. I was thinking about building some (dont have the money to buy) was wondering about the problems and what not i would have?

does anyone have any help with this

Yes, a dropped control arm is actually a raised balljoint You can modify stock control arms and make them dropped. all you do is raise the mounting point of the balljoint. If you say you are building some, it's all a matter of where you want the balljoint placed based on what size rims you would be running and what camber you would need to make them tuck