Fig. 1, left: The lines a and b presenting top and bottom of a wall (ABCD) of even heights throughout, converge to a common Vanishing Point (VP1) on the Horizontal Line (HL).
Fig. 1, right: Top- and bottom-lines of posts of equal heights and standing in line converge to a single VP2.
Fig. 2, left: The diagonals of the plane define its mid-point M.
Fig. 2, right: drawing further diagonals allow to create lines marking equal intercepts.
Fig. 3: A perpendicular line to the Ground Plane (GP) through M prepares the base to locate D - defining e.g. the end of the mid-line of the roof.
Fig. 4, right: Draw line through M and VP2 to create N, draw line from B through N to create Q, draw vertical through Q to create L. The resulting blue and yellow areas are of equal size, the distances AD and DQ of equal length.
Figures 5 and 6: The sets of diagonals of areas of equal size converge to Vanishing Points (VP) located on a vertical line to the Horizontal Line (HL).