Amperage generally isn't a problem when running shop tools at 220V.
The current is half what it would be at 110V, so 20 amps is usually
more than sufficient.
Likewise, having a long power cord on your tools is usually less of an
issue at 220V. Power (in watts) dissipated in the cord = I^2*R, where
I is current (in amps) and R is the resistance of the cord (in ohms).
Since current is half at 220V, the power dissipated in the cord is 1/4
what it would be at 110V. Thus, you can have a cord four times as long
as you could at 110V. And even then the cord wouldn't get as hot
because the power would be dissipated over a greater length.
I'd put a pair of standard 20 amp 220V outlets every 10 or 15 feet, fed
with 12/3 (plus ground) wire. Since your tools won't need a neutral
connection, you could also get away with 12/2 wire, but for the small
extra cost of the 3-conductor wire, it could potentially save you or a
future owner of your house some confusion and danger, since you'd have
to use the white (normally neutral) wire as hot.