The method we use in most of our projects is known as cob, monolithic adobe, or more specifically the Oregon Cob method. In areas where earthen building traditions are alive and well, it is a great idea to work with an experienced local builder. But if there are no living traditions in your area, the Oregon Cob method can help you create an effective method in a relatively short time.
Good building dirt is bad garden dirt, and vice versa. For a good earthen project, you want subsoil (the lighter or single-color layer underneath the dark brown topsoil); and you want mostly hard grit, sand, and sticky clay - not the soft, velvety silts and loams that make fluffy garden tilth.
For our typical earthen building projects, here are roughly the amounts of materials involved.
Base: Compacted gravel, 4" concrete slab, or reinforced floor suitable for waterbed / garage storage.
3-5 yards sand (or local sandy subsoil)
Perlite - 2 to 6 cu ft.
Barrel - 55 gallon or 30-35 gallon drum
Level (aluminum or steel, 24" to 48", for muddy work)
other suitable insulation (4-8 cu ft)