I worked up to a marathon very slowly. Ran a couple miles a day for a couple years and then I had a 4 1/2 mile route I ran for a year after that. I did not plan it this way but I had a decent base. I bought a book that gave suggestions how to train for the marathon itself. If I remember right it was a 2-3 month regimen. You would run lets say 4 miles one day and then 6 miles the rest and alternate that way for a couple weeks. Then increase the longer run a mile or two and continue to alternate where you have a long run and then a short run the next day building up to the 2 weeks before the marathon where you run about 18-20 miles on the long run.
