Walk his routes on the plan before you choose anything else
Spread the floor plan out and trace, with a finger, the journeys your large dog will make many times a day: entrance to water bowl, water to bed, bed to garden door, and the excited route he will take when visitors arrive. Those routes need width, because a big dog turning, shaking or passing a person in a narrow pinch point is how walls get scuffed and children get knocked. Avoid placing island units, console tables or door swings that cut across those lines, and check that doors on the route open fully rather than trapping a large animal in a half-open gap.
Specify flooring and finishes for the dog you have
New-build choices are easiest to change before they are fitted. On the dog's routes and in his main living area, choose hard, washable flooring that tolerates claws, water and the grit a large coat carries in, and keep pale, delicate carpets for rooms he will rarely enter. Ask about skirting and lower wall finishes in the entrance zone, because a big dog's shake throws water higher and further than most people picture. Plan a boot-room style corner if the design allows even a small one: a tiled section near the main dog door with drainage or at least a floor that shrugs off puddles turns muddy returns from a damage event into a two-minute routine.
Give him a sleeping place sized for a full stretch
Large dogs do not curl into leftover corners. Measure your dog lying fully stretched on his side, then protect a floor area at least that size in a spot that is draught-free, away from the busiest walkway, and close enough to family life that he chooses it willingly. Leave room beside the bed for a water bowl that will not be kicked as people pass in the dark.
Place washing, feeding and storage where they will be used
Decide now where a large, muddy dog gets washed. An outside tap with a hose point near the dog door, or a walk-in shower on the ground floor if the build offers one, beats carrying a heavy wet dog to an upstairs bath. Feeding for a big dog means bulky food bags and a bowl stand for comfortable eating height, so plan cupboard space beside the feeding spot rather than hauling food across the house twice a day. Gear storage, leads, coats sized for a large frame, towels big enough to matter, belongs by the entrance he uses, with hooks strong enough for heavy wet coats. Garden planning belongs in the same conversation: a gate that latches securely, fencing at a height and strength matched to his size, and a surface near the door that will not become a mud pit in the first winter.
Think through barriers and visiting life before furniture arrives
Decide where gates or doors will manage his access during parties, deliveries, workmen or a visiting baby, and make sure those barrier points exist in the architecture, with doorways that take a gate and a room he can retire to happily rather than being shut somewhere he hates. Test furniture layouts on paper against his turning circle and his favourite human-watching positions, because a sofa arrangement that leaves no dog-sized floor space in the family room will simply be rearranged by the dog. Planning these details while the home is still lines on a page is the cheapest dog-proofing you will ever do. Family members involved in the build can view that profile themselves via KinsLe Family Sharing.