This first thing to look for in a construction detail that can make or break a project is to look at it in terms of trades.
When you look at a detail, check to see how many trades are working on it. For example a wall that has stone, glass, and drywall with power and plumbing will need to be touched by 7 trades, possibly more. The wall itself would need a framer, a taper, and a painter. Then the stone mason, the glass fabricator/installer, the electrician, and the plumber. Now imagine if you did a wall that was only glass, and put power outlets and plumbing in the furniture? Now you deal with only one trade. A huge contrast in terms of labor, coordination and complexity. When trying to bring down costs - look to limit your trades. If you need to increase it - add more trades!
Glass is a long lead item, so if you get it right, you can order early with flexibility built in to it. If you procrastinate, or if your designer wants to go all the way to the floor, then you will spend on leveling the floor... or ordering a frame that adjusts with the movement of the glass.
Typical savings can range on the order of 5-10% of the job... nearly the entire design fee!
Was it the devil in the details or the angel in the details? It will make or break you for sure.
DETAIL 3
Most people think that stone and tile is the only way to make a bathroom maintenance free... but keeping this clean and sanitary is about as nightmarish as any other material, and arguably more!
Think about other things like industrial coatings on panels, and other simple ways to install these surfaces... Again, more ways to cut on labor costs. remember that a tile-setter is roughly 14/sf for labor only. then add your most favorite stone and you're looking at 20-50/ sf.
The cost of other types of panels can run the gamut of just a few dollars a square foot to over $100 dollars for a 4x8 sheet for laminates. The materials these days are endless...
Be sure to get creative on this. For one bathroom, I used corrugated plastic skylight panels secured with neoprene washers to horizontal 2x members which were bolted to uni-strut studs... A cheap way to make a great waterproof wall. I even back-lit the corrugated panel with LED lights for $50 bucks a string. Again... be sure you have a detail of this. Nowadays, I use a 3d model to show the contractor what I want... it's a lot simpler to communicate, and they get it faster! In another bathroom I'm using horizontal sheet metal, and in another flat seam roofing! All impervious to moisture as indicated by the code. But much faster to fabricate AND install. Big bucks!
Detail 5
Electrical distribution can be incredibly pricey! Light fixtures ALWAYS catch clients by surprise.
Very little attention goes into branch wiring layouts, outlet reduction... here's an example, a quad outlet costs just a little more than a duplex outlet, you get two more plugs, and for the electrician, most of the labor has to be done anyway. At $500 per outlet or switch drop, it makes sense to either put things on remote with smart switches, gang your outlets, and buy power strips (within reason) . how many power strips can you buy for a single outlet drop?
Most newbies go outlet crazy! They want outlets and switches everywhere. They are called convenience outlets, so owners go nuts trying to make their lives "convenient". Until the bids come in, and then they need to cut back the outlets. It's the $500 price per drop that kills you.
So the best bet is to go with fewer outlets if you can. Find other ways... use a power strip, or work from a collective. Charge your devices in a central area... Best to go with wireless switching, or smart switching when the job gets too complicated. Move toward digital for controls... Old school analog may be reliable... but you will pay dearly as tech controls get cheaper and cheaper, and the cost of an electrician's labor goes higher and higher. Be very careful with making outlets, switches, and lighting selections.
DETAIL 2
Check the plans for the baseboard detail and using trims. We worked on a bank that wanted cove and base trims all over the space. It was a local branch and they wanted to make it feel residential and "homey".
This was naturally drawn simply with a few single wall details. Innocuous until the trim package came in North of 70k. That's a lot on any job. And again, it costs more than the architect's fees. T
These types of single tiny details can carry a huge punch in the gut to your budget. Be ready to make compromises, or just choose a more modern, simpler look. What was the reason for such a high cost of just a few wood trims? The labor to install them. Seems simple enough - until you get to the corners. They MUST be mitered when the detail is intricate, and the cost of labor to apply the trims is nothing short of stupendous.
Look for simple clean, easy to build details. And if you don't see these types of details in the drawings.... ask like there's no tomorrow... because you need to be sure you know what you are getting!
DETAIL 4
Think of creative and fast ways to build instead of just looking at what looks nice. Your architect wants to make things beautiful, but still needs to cycle through different construction solutions to get you there. Make sure you budget for that chance.... because if you let the architect work through this... you'll find untold dollars (10'x's value) in proper planning and vetting. Rushing because you or your CO is excited about a project doesn't help bring the budget in... for every design solution that your architect does not have time to consider means that you will spend roughly 10x's that when you have to make that decision in the field.
Can you imagine how residential designers who don't draw stay in budget? Doesn't happen! They rely on the contractor (who strategically works on T&M) to quantify and order material with no details or knowledge of how it will all come together. You may save on drawing fees, but you will bay DEARLY as the designer and the contractor spend hours trying to "figure it out" in the field. Yikes! That's how budgets run away. Only minimal permit drawings.... but no detailing. It's the kiss of death, I tell you!
Invest in an architect if just to help you figure the details. It will help save so much when you get into the construction phase. It is literally a 10x investment.