Thre's Big And Then There's Globus Cassus

Wiki:

Globus Cassus is an art project and book by Swiss architect and artist Christian Waldvogel presenting a conceptual transformation of Planet Earth into a much bigger, hollow, artificial world with an ecosphere on its inner surface. It was the Swiss contribution to the 2004 Venice Architecture Biennale and was awarded the Gold Medal for the "best designed books from all over the World" at the Leipzig Book Fair in 2005. It consists of a meticulous description of the transformation process, a narrative of its construction, and suggestions on the organizational workings on Globus Cassus.

Being the Earth/World's antipode in many aspects, Globus Cassus acts as a philosophical model for the opposite-based description of the Earth/World and as a tool to understand the World's real functioning processes.

Waldvogel describes it as an "open source" art project and states that anyone can contribute designs and narratives to it on the project wiki.

The proposed megastructure would incorporate all of Earth's matter. Sunlight would enter through two large windows, and gravity would be provided by centrifugal force. Humans would live on two vast regions that face each other and that are connected through the empty center. The hydrosphere and atmosphere would be retained on its inside. The ecosphere would be restricted to the equatorial zones, while at the low-gravity tropic zones a thin atmosphere would allow only for plantations. The polar regions would have neither gravity nor atmosphere and would therefore be used for storage of raw materials and microgravity production processes.