While the buckler is an exception (making it the smallest shield in the game), each shield's block radius (the size) increases progressively with the level.
Currently there is no way to craft shields, but they can be purchased in the Store for varying prices. Better shields become available to purchase as the player progresses through the Time Chamber.
Arguably the most important aspect about shields is their benefit to Armor Class. The higher the players Armor Class, the less damage they take when hit by an arrow or target in the Time Chamber.
Shields also have a durability statistic, although it has no effect in-game. Shields are planned to be breakable in the future similar to that of blades.