Hakoniwa Oukoku no Craft Master

Hakoniwa Oukoku no Craft Master (箱庭王国の創造主サマ〈クラフトマスター〉) is a manga series by Rio Nanamomo. It is serialized in Dengeki Daioh.

Plot
An otaku programmer who spent the last three years creating the world he desired suddenly encounters a BUG; he gets depressed and just goes to bed. When he wakes up, he finds himself in the world he created.