Do i need a subpanel for a single circuit with less than 4 receptacles equaling less than 600 watt load. Washington state
You state in your comment that you plan to run conduit.
In that case, do NOT use UF cable. Use THWN wiring - the conduit protects it, and it's much easier to pull than UF cable. It may also cost you less, and it can indeed be easily upgraded if or when you or a later owner wants to upgrade.
12Ga should be fine for your planned use. If your use increased, pulling one more wire and changing the feed breaker to a two-pole 20A GFCI breaker and making the circuit an MWBC would double your available power at the building.