To build a wood-drying kiln, determine the size required, use 2-by-6 lumber for the floor's frame and 2-by-4 lumber for the roof's and walls' frames, and affix plywood for the kiln's walls and floor and a transparent polycarbonate sheet for the roof. Create doors and openings for the vents, affix the vents, and attach window fans.
Begin building a wood-drying kiln by selecting an appropriate sloping roof size. Ensure that the kiln is long enough to accommodate the length of the lumber and is of a width that leaves one foot of extra space on the lumber's either sides.
To make the floor and wall frames, cut lumber to the required size, and affix using joists at intervals of 16 inches. Create a doorway in the side or rear walls, and vent openings in the rear wall. When making the frame of the roof, space the joists so that maximum sunlight enters the kiln without affecting the roof's sturdiness.
To make the kiln's floor, place insulation between all joist pairs, attach 0.6 millimeter plastic sheet on the frame using staples, and affix plywood over it. For the walls, place insulation between stud pairs, and affix plywood on both sides of the frame using nails. For the roof, attach corrugated polycarbonate sheet to both sides of the frame using nails.
Apply aluminum or rubber-based sealant on the inner walls, and use black paint for the final coat. Use an exterior latex paint to paint the outer walls.
Affix vents in the rear wall openings. Use 2-by-4 lumber to make window fan frames. Affix these frames to the roof's frame such that the fan rests 3 feet under the roof and 18- to 24 inches away from the rear wall, and attach the fans in them.