Get an architect and pay. Design build is a more expensive way to go in the long run, it takes longer......because it is usually less efficient and results in changes during construction that could have been avoided. Pay for the plans, the specifications of materials and the elevations. And let the builder.....build.

Hire an architect for well specified plans first. Cost plus is the way to go for a true custom home, but that assumes that you yourself can restrain yourself from indulging in luxury for everything. If you don't have good budgetary restraint to stay within the $300-$500 a square range of a true custom, then you really should think about buying an existing.

I imagine the cost may depend on where you live (a $1m house in Vancouver is half that somewhere else), but here's our experience with planning new custom home construction and alternatives we've considered.

My husband and I are working with a fantastic architect in AZ, who recommended we hire an interior designer, choose a builder, and consider the option of acting as the general contractor on the project. Being our own GC entailed meeting the subcontractors (to whom the builder would introduce to us), tracking them in a spreadsheet, and paying their invoices, as well as staying on top of things during the construction, which we would do anyway. Acting as our own GC was an option to save the 20% of the total cost and possibly be sure things were to our specifications and not lost in translation (the architect and designer would also consult to help us). Our architect made this part of the conversations with builders we would meet.

The contract for the architect to design the home with all his wish list dream-home items, including all the drawings and consulting with the HOA, getting permits, looking at the land, etc. was $50K, not including expenses like filing and permit fees. He handled all this beautifully, especially considering a finicky HOA and a site that required the home be designed for mountainous topography and granite outcrops, protected sagauros and endangered wildlife.

The design is a 4,000 sf home in Tucson (4BR/5BA, media room, huge kitchen, open plan with great room and a glass wall transitioning indoor-outdoor living spaces, infinity edge pool, fountain, outdoor kitchen, fire pit, custom seating -- all dreamy) There's an additional 3,000 sf in outdoor living spaces and a 4 car garage. The architect's first design fit the bill for timeless, unique, stunning and more importantly it used every inch thoughtfully and intelligently. The design process has been incredibly collaborative.

Our interior designer, found here on Houzz, capped her fees at $15K to design the entire interior package (based on the above specs), including finishes, electrical/lighting plan, kitchen design, the works. It also included high quality state of the art renderings, which looked like pictures. (Helping us choose, shop and arrange our furnishings when we're ready to move in is a separate contract). Our designer is also an architect, which we believes saves us on a lot of back and forth (she can read the engineering and architectural drawings so that she doesn't suggest something that requires structural changes). She gets along with our architect beautifully.

Conceivably then, the architect's and interior designer's combined work to design the exterior, landscape, pool and interior package of the house would have cost a total of ~$65K.

I say conceivably, because the original completed design (ready to be built) predated my husband meeting me and was designed for a forever bachelor. The year his original project was to be built, my husband met me. After we got married, we made changes over the past two years to the original bachelor-home project to make it a multi-generational home for two huge families and with two separate full offices. As the other project was deemed finished before we began making many significant changes/additions, we entered into a separate design contract with both the architect and designer, with the understanding that consulting during the build phase will be a separate contract. This makes sense for us because of our spread out timeline. We're not in a rush.

PS I should add that we've also looked at semi-custom builder homes as an option, as well as houses to renovate. The former takes about 9 months to build anyway (same time frame as building a custom home after it's fully designed) and customization costs weren't clear. The houses would still look like other homes to an extent. We also wanted something our years-long research has convinced us doesn't exist all in one existing home, designed to our taste and style. Renovating an existing house doesn't quite make sense for us because our land lot is special to us. Also the flow would not be as completely suited to us, and how we believe modern families like to live, should we want to sell it way off in the future. We have seen cool houses with similar flow to ours but only custom homes outside of our budget and only in pictures on Houzz (Most of those are square or rectangular boxes, which ours is not).

I know this response is a year after you posted-- and could use some editing -- but hopefully this proves helpful to people in similar situations.