On May 29, 1787, Virginia delegate Edmund Randolph proposed what became known as "The Virginia Plan." Written primarily by fellow Virginian James Madison, the plan traced the broad outlines of what would become the U.S. Constitution: a national government consisting of three branches with checks and balances to prevent the abuse of power. In its amended form, this page of Madison's plan shows his ideas for a legislature. It describes 2 houses: one with members elected by the people for 3-year terms and the other composed of older leaders elected by the state legislatures for 7-year terms. Both would use population as a basis for dividing seats among the states.
The Virginia Plan went through several revisions before it was finalized. These "Variant Texts" of the Virgina Plan are available at Yale Law School's Avalon Project.