nest, living quarter in tree
巢 centers on a constructed dwelling place in a tree: a nest or a living quarter built among branches.
巢 combines 巛 (a pictograph of a bird's nest or flowing lines) with 果 (fruit), likely suggesting a nest as a fruit-like structure in a tree. The exact historical development is uncertain, but the character visually represents a nest in a tree.
The top 巛 looks like twigs and branches woven together, and the bottom 果 is a fruit. Picture a nest built like a fruit hanging in a tree: a living quarter made of twigs.
For ソウ, imagine a bird sewing its nest together with twigs: sew -> ソウ, and the nest is a carefully sewn home in the tree.