Construct a sturdy rectangular frame that will house the entire heater. This frame appears to be made of metal, which is durable and conducts heat well.

Line the back of the frame with insulation material, like the rigid foam board shown, to minimize heat loss. Depending on your choice of venting size, drill holes for venting.

We added handles on the side to make moving it easy.

Collect and clean a large number of aluminum cans. These cans will act as the heat absorption medium.

Remove the tops of the cans, and drill a hole in the bottom of each one for air to pass through.

Stack the cans in vertical columns, securing them to each other. This can be done using a strong, heat-resistant adhesive. Each column acts as a conduit for air to flow and be heated.

I used caulking and paint that would handle high heat.

Ensure everything is securely attached and sealed.

Paint the cans black (if not already colored) to maximize heat absorption.

Install an air intake at the bottom and an air outlet at the top of the heater. These can be ducts or pipes that allow cold air to enter, get heated as it rises through the can columns, and then exit as warm air.

Cover the front of the frame with a clear glazing material, like Plexiglas or glass. This creates a greenhouse effect, trapping solar energy inside to heat the cans.

Seal any gaps or edges with weather-resistant seals to prevent heat loss.

Optionally, add additional insulation around the sides of the frame to further reduce heat loss.