Building box ... have question or two

Building a box 4 feet wide 6 feet tall and dont know if i should go 18 inches thick or a little thicker like 21 inches or 24 inches... this is for moms on bottom and babies on top... my other question is im going to make it pretty air tight but i have no clue what kind of fans to use for ventilation and where i should put them... im building a 4 feet wide by 5 feet tall by 2 feet thick box right next to veg box for flowering... and i need to know where i should install the fans at in it... id like to hook it all up to a carbon filter with a vortex for smell... can someone who has built box setups please help out and inform me on what i have asked.... thanks

Build the boxes the same depth, at least 24".

Flower in the taller box.

PC :smokin:

put the extraction fan inbetween the lights, or if just one light ideally above the light.
You will want some oscilating fans as well to move the stagnent air. They should blow the top and bottom of your canopy.

made the first 24 deep x 4.5 ft x 6ft tall.... had to make it a little wider to fit fuoros.....went with two shelves... was gonna go with three but need some room for moms

ran new line off its own breaker and installed gfci outlets for box/boxes.... need to make some doors for first box but still trying to figure out the best way to make them.... any sugestions on building doors??? once doors are done then gonna work on my ventilation setup.... is the rule of thumb to use metal ducting or tin flex ducting for running exhaust off of cooltube? and using either metal /flexible or pvc for intake? any do`s and dont`s for ventilation?