This gnome spellcaster dons some animal pelt, carries a cat around on his shoulder and carries a staff arcane focus. He smooths his epic moustache and beard. He wears some simple clothes. This basic getup is similar to most spellcasters who can't wear armour like wizards, warlocks and sorcerers.
 
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)