I have just finished the cage! I know it is only 2x3 for two guinea pigs and another 2x3 for one (long story, see this link
https://www.guineapigcages.com/forum/about-guinea-pigs/26289-what-do-i-do-lone-pig.html?highlight=lone).
My parent's wouldn't stretch to a 2x4, so my poor piggies will have to c