Fire Engine Cake

[BeckaJayne]

Hey everyone, just looking for a bit of help! I've been asked to make a fire engine cake and want to do a 3d one instead of just the tin one! Im just struggling on figuring out how to get the height of the cake and was wondering which way is best using the tins i have!

I have an 8" and 6" square tin but if i use the 8" tin i'd have to bake 3 cakes?

If i use a loaf tin (9"x5") what recipe size would i use....7" square?

Thanks in advance!