This pattern is worked mainly in sc. It includes intarsia crochet on the bonnet and side windows, but includes a full photo tutorial for those unfamiliar with this technique. It requires a lot of sewing up, and embroidery chain stitch. Any yarn may be used, as long as all colours are of a similar weight and the hook is selected to give a firm fabric. Using DK yarn and a 3mm hook, my finished tractor measured approx 21 cm long. For the tractor shown I used:
80m green
100m black
120m charcoal
60m yellow
6m grey
50m silver

It requires stuffing, foam rubber is preferred to keep the shaping correct.