Hi, before using sugar soap on the mould try using Dettox mould and mildew remover. You don't want to be moving the mould around the walls and doors before you start, better to kill it off first. After doing this use the sugar soap as directed on the box on the walls and doors then wash off. This will get rid of the grime and grease that may be on them along with the marks from the mould. Sugar soap is used to help prepare things prior to decorating and I don't think you can make your own. After this prepare woodwork and walls as usual with glass paper etc then decorate. A tip if you want nice smooth doors is to use a Tack Cloth on them just before painting. This will pick up all the very small bits of dust on them that can spoil the finish. Good luck. Shed.