flesh (something) out or flesh out (something)
to make something more detailed or bigger
We worked hard during the weekend to flesh out our agreement.
Amazing Treehouses From Around The World
Alnwick Garden Treehouse
This massive structure is located in the UKs Alnwick Garden and was completed in 2005. Due to the houses size, a network of wooden braces must support it, so its not a treehouse in the traditional sense of the word. However, it stretches high into the treetops and several trees grow right through the floor and up past the roof. The building is home to a restaurant that serves gourmet local food.