Mark a point on the center of your paper. Label this point "VP" as an abbreviation for vanishing point (a point where lines on a 3D box will eventually converge to).
Draw a rectangle that is 2 inches wide and 1 inch high starting at a point on the lower left edge of your paper. Label the lower left vertex of the rectangle as point "A," the upper left vertex of the rectangle as point "B," the upper right vertex of the rectangle as point "C" and the lower right vertex of the rectangle as point "D." Label the line that connects point "A" and point "B" as "AB." Label the line that connects point "B" and point "C" as "BC." Label the line that connects point "C" and point "D" as "CD." Label the line that connects point "D" and point "A" as "DA."
Draw a line from point "B" to point "VP." Label this line "BVP" Draw a line from point "C" to point "VP." Label this line "CVP" Draw a line from point "D" to point "VP." Label this line "DVP"
Draw a line 1 inch above line "BC" that is parallel to line "BC" and starts on the line "BVP" and ends on the line "CVP." Label the start point on this line as "E" and the end point on this line as "F." Label the line "EF."
Draw a vertical line from point "F" to the point where this line intersects with line "DVP." Label this intersection point as "G." Label this vertical line as "FG."
Erase the line that extends from point "E" to point "VP." Erase the line that extends from point "F" to point "VP." Erase the line that extends from point "G" to point "VP."