Bygg hus med Mulle Meck is the fourth game featuring the children book character Mulle Meck (known as Gary Gadget in the US). After building cars, boats and air planes in previous games, this time he is building a house. His old house has been demolished in a storm and now the player needs to help him build a new one.
As in previous games, Mulle's garage is full of different parts that can be combined in different ways to create the house that Mulle always have dreamed of. Objects that can be used is added to a building book and to construct the house the player simply drags and drops the different walls, floors and roofs he wants to use onto the scene. The house can also be decorated with different furnishings.
The player can leave the construction site and go out and explore the world around him. By doing so he will meet several different characters that he can do missions for. By doing missions he can get more parts and furniture for his house. The travelling is done both by car and by boat.