How much land should be given to the government?

No land should be given to the government. If they want land, they will simply take it.

"Eminent domain is the power of government to take private land for public use. This power is limited by the federal Constitution and by state constitutions -- when the government does take private property for public use, it must fairly compensate the owner for the deprivation."

However, it's the govt who sets the price and they may say it's worth 10 percent of the actual value.