It was just that the three insisted for Erik to stay there. For obvious reasons... Not that one could blame them...
Erik had built only one structure. It wasn't very big, but it was strong and well-made. The most important aspect of it was that the building was sturdy and comfortable. It could easily stand up to bad weather and keep the people inside cozy in the meantime. The house had roots, and it would be hard for storms to destroy it.
Erik used his Plant Master brain crystal power to make the vegetation grow into the shape of a house. He guided trees and vines to form the walls and roof.