But you need to isolate the pressure around the body from the neck down. For such an enclosure you can use modern materials with high tensile strength like fiberglass but you need to mold them in a sealed manner on a large scale. Very impractical to do in a garage without experience and tools for laying fiberglass matting, or welding in the case of steel or aluminum, which are too heavy to be practical in a home I think
https://en.wikipedia.org/wiki/Barotrauma#Ventilator-induced_...:
”Barotrauma is a recognised complication of mechanical ventilation that can occur in any patient receiving mechanical ventilation, but is most commonly associated with acute respiratory distress syndrome. It used to be the most common complication of mechanical ventilation but can usually be avoided by limiting tidal volume and plateau pressure to less than 30 to 50 cm water column (30 to 50 mb)”
⇒ a mechanical lung should support about 500 kg/m². More than your average chair or table, but not infeasible.