Actually you usually build
first followed by
then tank. Land the q and catch the boomerang for the cd constantly...i mean spam it. It is free. Never use the jump unless you are escaping a gank, escaping a bad trade, or you know you have the kill. Most of the time early game don't try to fight as mega gnar with your lane mate. You are super squishy and slow in mega for early. Also, your abilities in that form have LOOOONG cds. So extended fights usully wont go your way.
You are a lane bully in mini form and a team fight nightmare late in mega.
Think of it as a short range ADC in lane and a CC tank as mega gnar late.