Cage My mom is so unreasonable!

so, i posted on here before asking what to do about the hay and bedding sruff... so i asked my mom if i could do that. she said and i QUOTE: "No, because that will be more room. what are you even going to puyt in there?" "bedding!" i said. "no youll just be spending more money" what does she care?? I'm the one who pays for them! Its not even her money though! she always forgets my allowance! this is my birthday money, and when I sell things money! Also, when we were building the cage, I said: "no wait mom a 2x3 is too small I though i was getting 2 and that size is a 2x4 at minimum" shes like "oh well you can make it bigger when they get older because thats like the size of a petstore and they have 5. plus thatll take up like half your room" yeah idc all i do in here is sleep... How do i convince her to let me have hte bigger cage?