Oh the ready to roll icing is easy peasy.
trim the hump off the top of the cake/cakes if you are cookign vic sponge style.
buttercream filling turn the top cake upside down so you have a totally flat top to the cake.
place on a cake board.
put a thin layer of buttercream on the top and sides of the cake - take your time to get this quite smooth.
set the cake to one side.
roll out the icing as you would with pastry but use icing sugar instead of flour so it doesn't stick.
turn the icing at 10 minute intervals (space NOT time - if you imagine it to be placed on a clock so that you roll out a circle) iykwim
once you have it so that it is bigger than the diameter of the cake board, use the rolling pin to pick it up and lift it from the back to the front of the cake so you can see if it is centralised.
to get it to sit smoothly against the cake without creases use one hand to pull the icing out like a skirt over the board whilst gently with the other hand tucking it into the side of the cake. work round the cake and you will find that it has covered with ease.
AND - I will send you plenty of leaves and blossoms to stick over any scarey bits that didn't work as you expected.