Take pictures, then measure with a tape and calipers and start modeling.
If you want it to be an exact replica, get the specs and dimensions, lol
If not, take some ballpark measurements and roll with it.
Just depends how accurate you want your model to be.
Start with a simple component - say the fuel cap, model as best you can and attach your *.sldprt file here for suggestions on modeling techniques.
I would project about 6 months for modeling the entire bike.