How to Build a Dungeon: Book of the Demon King is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

"I do not trust humans. They’ll betray you without fail.” Aur, the man who had obtained the ability and right to become the Maou at the end of his life of research. Summoning the succubus Lilu, he then sets out on creating his own domain, a gigantic labyrinthine dungeon… The misanthropic Maou taking on the world, the curtain rises on a dark harem fantasy! ...