I've been thinking about building a shop, 30x40x14

I was thinking about forming and pouring a 6" to 12" high wall around the parimeter (to compinsate for drop in grade) and then filling in compacting and then pouring the floor. Then building the walls on 4' center like you would a house using 2x6x14's

The advantage to this will be...

1, I would have to worry about trucking in fill to level the whole area.
2, cost would not be any more than using 6x6 on 8' centers
3, on 4' centers, this will allow me to use 8' sheet of plywood for interior
4, For all practicle senses, I could build the walls by myself... infact do most all of it alone

What do you think ?