You can sometimes purchase Oriented Strand Board (OSB) in sizes of 2 x 8 ft that is tongued and grooved. The usual size is 4 x 8 ft, the 2 x 8 ft size is intentionally sized to fit through an attic door. The tongued and grooved edges allow the pieces to interlock. I floored an ttic attic using this approach.

You can sometimes purchase Oriented Strand Board (OSB) in sizes of 2 x 8 ft that is tongued and grooved. The usual size is 4 x 8 ft, the 2 x 8 ft size is intentionally sized to fit through an attic door. The tongued and grooved edges allow the pieces to interlock. I floored an ttic using this approach.