I made this photo while visiting my family on a farm in Middenmeer
As you can see the nest was built on a rake hanging on the wall in the Barn.

Barn Swallows build solid nests out of mud pellets brought by the beak full from puddles and river banks,( you can see the mud spatter on the wall) combined with dry long grasses.
With both parents participating, these pellets are arranged much like bricks to form half-bowls or saucers.
Up to 1,000 trips may be made to bring the mud balls to make the nest.
The nest is lined with fine grasses, as you can see in the photo, hair, curly feathers.
Barn Swallows usually make their nests in man-made structures that provide shelter (because the mud would disintegrate in the rain) and warmth.