Apart from the engineering aspects of you theory, have you given much thought to the logistics of operating such a construction?
It seems to me that the volume of grain needed to make such an endeavour worthwhile would be massive. It would take an awful lot of people an awful lot of time to transport enough grain to one site. Then it would take them an awful long time to get it back to where it was needed. They're on foot remember, probably carrying the stuff on their backs. There's got to be a certain radius around the site, beyond which it would be impractical to haul your grain. The area within this radius would presumably be the area within which you'd be able to recruit for building. It should be possible to indicate the population density needed, then by comparing the population density with the avilable amount of grain you could feasibly have grown in such an area, you'd be able to work out if you could feed enough people to make such a contrivance theoretically possible.