What is the best but cheapest way to add a pitch to the roof of a mobile home?

Ok I am purchasing a mobile home and the roof has some leak issues, I was going to cover the whole thing with bitchutane and shingle it, but someone told me to use tar paper and shingles I have also decided it is too flat and needs a better pitch so what is the best pitch and the cheapest way to add one (single mom raising a 5 month old on a limited budget with a pretty good knowledge of construction, roofing etc)