Make sure the chocolate is cooled before it is added to the egg mix or it will go grainy. Don't use anything other than a swiss roll tin otherwise you won't be able to roll it at the end. Make sure the cake is completely cool before attempting to roll it. The chocolate roulade will crack, if the cracks are really big then push them together with your hands as it will still be pliable. The cracks and lumps and bumps of a chocolate roulade are all part of the charm!