> For the complete documentation index, see [llms.txt](https://orbcity.gitbook.io/orbcity/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://orbcity.gitbook.io/orbcity/building/construction-system.md).
# Construction System
#### A building's construction system is responsible for supplying building NFTs to the ecosystem. To upgrade a building's tier, buildings of the same tier are used as materials (=demand). The number of buildings is reduced by the upgrading system, and the construction system is there to supply them again. However, only building owners (who are granted a construction license per building) can build new buildings, and Lay 007 Robot and $Orb are consumed as resources to construct new buildings.
{% hint style="danger" %} **Note: Keep in mind that all tokens and NFTs spent on the upgrade are irrevocable and non-refundable.**
{% endhint %}
---
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