I am one who likes to make stuff.
If you search diy evaporative coolers you will find many examples of small ideas.
I chose to buy a secondhand unit and fit that, because it was so easy.
BUT, I have seen wind towers in the middle East and India where air is drawn out of the house via the tower and replacement air into the house is drawn from a cool courtyard with ponds.
cooling towers are similar but work backwards by being the source of the air into the house.
Membranes are installed high in the tower, water is applied to them and air is drawn through the membrane, down the tower and inside the house.
The is drawn down by ventilation systems which can draw air through the house.