Stupid Question from a newbie

Ok... I'm sure most anyone that reads this will think I'm an idiot, but
I'm so curious...

Could I build an ultralight airframe from EMT (electrical conduit) from
the local hardware store? I know that welding it would be inadvisable
due to the fact that it is galvanized (although I understand that
galvanizing can be 'stripped' thru use of an acid solution) but are
there other differences between standard hardware store emt tubing and
the steel tubing recommended for aircraft construction?

And now for the REALLLY stupid question... what about using PVC tubing?
I know that PVC is much more flexible than steel or aluminum tube, but
could it work? The reason I ask is because I keep thinking that if we
once made airframes out of wood, then wouldn't PVC be just about as
strong and more durable (long lasting?).

Rich