I am pretty sure I want to use some 6x6 pressure treated wood to make the
beds.


Be extra careful when using pressure treated wood. Myself, I wouldn't touch
it with a ten-foot pole. Google for "pressure treated wood" and you'll see
what I mean. Besides leaching harmful chemicals such as arsenic in the soil,
there's tons of other problems it causes. Touching it can give you rashes,
it can cause arsenic poisoning in children (people used to build play
equipment with it) and adults just from handling it. It's at it's worst when
it's cut or burned, when the sawdust or smoke is breathed in. It causes a
range of problems from cancer to asthma. It is also banned in several
countries.

I'd hate for you to regret your decision later, after you've put it in. If
you still decide to use it, be very careful.