I disagree completely. I'm no carpenter. Anyone who can use a chop saw, drill, speed square, level, and caulk gun can build a tank like I built.
You probably need a better set of skills to build a 240. A small tank like that is more dependent on precision measurements. Not that you couldn't build a 240 with 2x6 walls, but it wouldn't be practical.
In my opinion, unless you already have the glass from another tank i.e. like my 90 gallon expansion project, it's a complete waste of money and energy to build something so small. Bare minimum, a 500 gallon would be easily done. I'd recommend 750-1000 with the same piece of glass you'd use for the 240. Make it the same height and you have no different pressure.
Anyone who is willing to ask questions and listen to some advice can build a big plywood tank. Don't be hardheaded about it. Ask why. If the person can't explain why, then you probably shouldn't listen to them.