This dwarf spellcaster dons some animal pelt with goat horns on the hood, and spots an epic beard. He wears some basic armour since druids can't really wear or carry anything metal. This basic getup is similar to most spellcasters like wizards, warlocks and sorcerors.
 
Here's a D&D size chart for reference, and if you ever wish to custom print a different size of this design (tiny and small options are not available for printing):
Tiny - 2.5ft x 2.5ft or 1/4 squares x 1/4 squares. Base size ~0.7cm diameter. (eg. most animals)
Small - 5ft x 5ft or 1 square x 1 square.  Base size ~2.5cm diameter. (eg. halflings, dwarves)
Medium - 5ft x 5ft or 1 square x 1 square. Base size ~2.5cm diameter. (eg. most humanoids)
Large - 10ft x 10ft or 2 squares x 2 squares. Base size ~5cm diameter. (eg. trolls, beholders)
Huge - 15ft x 15ft or 3 squares x 3 squares. Base size ~7.7cm diameter. (eg. dinosaurs, giants)
Gargantuan - 20 ft x 20ft or 4 squares x 4 squares. Base size ~10.2 cm diameter. (eg. ancient dragons)