Level the ground where the shed will be located. Cover an area that is a minimum of 10 by 10 feet with a 2- to 3-inch depth of gravel. Make sure the gravel is level.
Construct the 2-by-10-foot and 8-by-10-foot flooring frame sections. Put the two sections together and secure them with eight 3-inch nails per 2-foot section. Drive four nails through from each side, staggering the placement to avoid hitting the nails from the other side.
Set the 4-by-4-inch runners on the gravel perpendicular to the inner floor frame boards. Set the floor frame on the runners with the small frame section at the back. Space two runners 8 inches in from the outer frame boards at the front and back of the shed. Place one runner underneath where the small section and large section of floor frame are joined. Center one runner halfway between where the small and large frames are joined and the front edge of the shed floor.
Measure the floor frame diagonally from corner to corner to make sure it is square. Both diagonal measurements should be 167 3/8 inch. Attach the floor frame boards to the runners where they intersect. Make sure the floor frame is level before installing the floor panels.
Install the floor panels rough side up beginning with the first large panel in the front right corner. Secure it with nails spaced 6 inches apart around the edges and 12 inches apart along the floor joists. Follow the same steps to install the remaining floor panels.
Construct the frame for the back wall of the shed. Attach the wall panels to the frame. Lay the completed back wall on the ground behind the shed floor. Assemble the side and front walls using the same procedure.
Lift the back wall into place on the shed floor and secure it on the left side with a 1-by-4-by-96-inch board as a temporary brace. Secure the back wall to the shed floor with nails driven through the bottom edge of the wall panels into the floor frame. Drive two screws at an angle through each wall frame stud into the floor frame.
Lift the right side wall into place. Fasten it to the back wall at the top and bottom corners. Finish securing the side wall to the back wall with nails spaced 6 inches apart. Drive nails through the bottom of the wall panels into the floor with two nails spaced evenly between each wall stud.
Remove the brace on the left side and install the left wall with the same procedure as the right wall. Lift the front wall and fasten it to the side walls and shed floor. Install the lower gable trim on the front and back wall panels.
Assemble the four rafters and attach them to the wall studs with 3-inch screws. Assemble the two loft joists and install them, attaching them to the last two rafters toward the back of the shed with 3-inch screws.
Place the loft panel over the loft joists. Secure it temporarily with one 2-inch nail at each corner. Install the roof panels. Secure the loft panel permanently with one 2-inch nail every 2 feet.
Assemble the door and install it on the front of the shed. Affix two collar ties to the two rafters closest to the shed door. Affix the horizontal gable trim over the gable panel seams on the front and back walls of the shed.