credit for skyscraper_big.png and skyscraper_small.png goes to:
https://www.deviantart.com/nicnubill/art/Sci-Fi-Gates2-467531375
created by 
Caitlin NicNubill

floor.png and steel-wire.png are color shifted factorio images.

skyscraper-shinra-tower/icon.png was retrieved from http://finalfantasy.wikia.com/wiki/Shinra_Electric_Power_Company
and is (c) Square Enix Holdings Co., Ltd. from Final Fantasy VII