Should i do this for my guinea pigs?

see my dad and i built a small cage for my 3 female guinea pigs and they live in a 1.5 x 4.5 grids cage see i want them to have a really good life but i asked my dad if 2x5 grids was big or small. and he laughed and said there was no damn difference(exact words btw) and then my mom and him was just like they are just dang guinea pigs they don't need a mansion! And then i went upstairs but you know these piggies are not just guinea pigs they are 3 months worth of research my birthday gift and my hopes! i know it may seem i am obsessed with guinea pigs but i love them! so anyways should i save up my money to buy the coroplast and fleece needed. and do it behind my parent'sback?