Farm vehicle I build outside, turning into earth-mover? (4,4)

'i build outside turning into earth-mover?' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'farm vehicle' is the wordplay.
I cannot quite see how this works, but
'vehicle' could be 'quad' (I have seen 'sporty vehicle' mean 'quad' so perhaps 'vehicle' could also mean 'quad') and 'quad' is found within the answer.
The remaining letters 'bike' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?