Don't be Fooled
The floor plan has to be complete, the interior and the exterior needs to be planned, and the type of materials has to be chosen.
Same as writing a novel. You have to prepare your characters, build the world where the story will take place, and plan the plot. In that way, once you started writing the novel, you will never get lost. But, sometimes, authors experience what they call a writer's block.
It's a period where an author can't think of what to write no matter how hard he tries. This phase is the hardest for any author, and it is what Henrey is experiencing right now. For days, he's been trying to think of a plot for his next book, but no matter what he do, he always comes blank.