The skin will get hard as wood and have a yellowish brown tint to it.. I usually leave them on the plant to dry..

Well if that works for you, I will do just the same

I cut birdhouse gourds off of the vine when they are big. Make sure there is some stem attached, otherwise they rot at the stem site. I leave them outside but on a a pile of leaves or somewhere where they don't touch the ground. They take more than a month to dry. They can get some really interesting mold patterns on them. If you can get the plants to grow up a trellis or into a tree, the gourd necks can get really elongated if they are hanging free. I have grown them successfully for 4 or 5 years and have made lots of birdhouses. They make great gifts, however, I have to confess, I have never had a bird nest in them in my yard. They frequently take out the fluffy stuff inside of them for their nests.

i have yet to grow these, i get mine at the fall market, i dry them by saving egg cartons, and lying them on the cartons, next to the heat vent over the winter. i make painted rattles out of them, i sand them lightly, and shellack them with the natural color and pattern each produce as they dry.