When we did this  (at the high school I work at) my original plan was to borrow one from a local dance company. We had very little space as well. It would sit just off stage until needed, then be pulled across the stage and then right  off the stage and hidden in another room immediately.  That fell thru at the very last moment so we just used the illusion of one  We used a cut out  that sat half off stage.(hated the way THAT turned out)

If you are going to make one though, what about paper mache over chicken wire (like for a parade float) You'd have control of the size, say only big enough for Cinderella to sit in. FG can walk along side if needed. As for storage space, do you have a place off stage even if just a hallway, that it can be  put in right after it's used? Just roll it across and out all at once. Just a thought

Hope that helps.