I originally though I wanted 20"x30" build area, but ended up trimming one side to fit the space I had to put the machine into. If I want to do longer pieces, I can slide them through and do them in 2 (or more) sections/jobs.
I made mine that big. 25" by 37" work area. It will work at that size, but it is big.
Bigger is less rigis, which means limited when cutting harder materials. I wouldn’t try aluminum on mine at this size. I’m going to try cutting it down to a smaller size in order to increase the rigidity. I ended up also building a LowRider in order to maintain the larger format, but it measn that my machine room is a little crowded.