Eisen placed brick onto brick, stacked log onto log, and connected all of them intricately with different techniques. In some parts, they were just connected by placing the different parts onto each other in a way that it was impossible for them to fall, in others it was done by really hammering certain pieces together with thick nails.
Luckily, Argalan had given Eisen a blueprint of what this building was supposed to look like, so he was able to use his Crafter's Soul skill to create a visualization of the building for himself that he could use as a guideline that not only he himself could follow, but so could his Mane Doubles as well as his Elemental Spirit.
Since his Mana Doubles could think for themselves just so slightly until now, as long as Eisen gave them specific commands that were supported by the whole visualized structure, he didn't have to worry about what they were doing for the most part.