I am watching four nice birdhouse gourds growing in my gardens. I'll pick them when the stems dry and turn brown or before a frost. They're not quite ready yet.
I looked up what to do with them and found this nice site:
When dried, these gourds are nearly as tough as plywood... it may take anywhere from 3 months to a year before gourds are completely fry. After picking, set gourds on several layers of newspaper in a warm dry place. Hanging them in a sunny place works well too... don’t put any holes I the gourds at this time or they will rot.
While curing, black, white and gray mold appears. This is a natural part of the drying process.... gourds that become soft or wrinkled should be tossed...
Gourds are completely dry when the seeds rattle inside... scrub with a stainless steel pad in warm soapy water to remove mold. Drill entrance holes for cavity nesting birds, removing the seeds through the hole... Holes should be 1 ¼” for house wrens, 1 ½” for bluebirds, and 2 ½” for purple martins... Add smaller hole at the top for hanging and in the bottom for drainage.
You can custom paint each house or use wood burning tools to decorate... Consider hanging a collection of gourds together for swallows or purple martins.
Here's a quote I found at the same site:
"When the world wearies and society fails to satisfy, There is always the garden."