Move the stand-ins around the ground plan to discover what arrangements work. Making a mid-century modern couch work in a Colonial manor house requires a certain skill set. To avoid the Alice-in-Wonderland effect, make sure the design includes strong, vertical architectural elements such as a chimney and towering windows. A house with no character is just a shell; without an interior design, it's not a home but a collection of parts. The first thing you need to know about building a house with an attached home is that both structures must be built according to code. There are different codes for residential construction and for commercial buildings. The most important factor in deciding how to build your house is finding a structural engineer who knows how to apply your house's particular design within the requirements of the general building code. For example, walls should be able to support the weight of people walking along them without collapsing. Floors should be stable enough to serve as a foundation for other parts of the building. Windows should be open to the air outside but closed off from the inside by security bars or glass if needed for privacy. Doors should allow heat and air exchange while keeping out pests and the weather. After code approval, you can move on to choosing materials and working on the floor plan. If you're building a new house from scratch, this may mean hiring a architect or designer to help you create something unique.