The traditional project delivery method used by general contractors and architects is the design-bid-build. This approach to a major home construction means finding an architect and a designer and first paying them to develop plans and designs. This is all while having no idea how much it all might actually cost to build. After the plans are completed, as the home owner you are now responsible for finding qualified contractors to bid on the plans produced, hoping they will take time to quote competitively to offer you a reasonable price.
In this case, design and construction services are split into separate entities, separate contracts, and inevitably separate jobs entirely. The owner must manage two separate contracts and liaison between designer and contractor. You will be responsible for settling disputes between designer and contractor, designer and subtrades, subtrade and contractor, etc. This also leaves opportunity for each party to blame each other, leaving you, the client to deal with it.