Wi-Fi New Construction - Network Sockets/Cables

With reinforced concrete ceilings, one should probably aim the antennas downwards if possible.

Since the radiation characteristics differ for each frequency range, the orientation of the antennas is always relevant. That means where antennas work better attached to the housing of the IAD (commonly "router") in wall mounting, they do so accordingly angled or vice versa in ceiling mounting. What laypeople also often forget is that interference can cause more disturbance than shadowing, and that excessively high levels can lead to similar disruption patterns as too weak levels. Therefore, for example, dropouts can occur where two repeaters interfere with each other or where one is too close to an antenna.

In concrete construction, you can count on one access point on the ceiling per room. In larger rooms, more than one may be necessary. Here, frequency and signal strength must then be controlled. However, this is rather rare in single-family houses.

Does anyone here have a drywall and problems with Wi-Fi coverage in that room? I have a lightweight wall upstairs. I would now spontaneously position an access point in the hallway, centered on the ceiling. Or should anything else be considered?

What should the access point cover? APs belong where most clients are and where the most speed is needed. For example, living room, office... There you need the fast 5 GHz network. With a (drywall) wall in between, you will probably only have a weak 5 GHz signal or none at all. The slower 2.4 GHz network reaches further or is less "blocked". In the guest bathroom in the hallway area, fast internet is not needed. Even for Netflix in 4k, about 12 Mbit is enough. Better to plan for one more connection. If the coverage is not satisfactory, you can simply install another access point. And please don’t start with mesh or repeaters. That has no place in a new building.

On the upper floor, all rooms (except the bathroom) are bedrooms and possibly offices combined. For each room (except the bathroom), a double RJ45 socket is planned. I didn’t want to plan multiple APs now, so probably one in the middle of the hallway is sufficient, and if necessary, a second access point can be installed later via a data socket. I’m not even sure yet whether the drywall actually "blocks" that much. That’s what my question was aimed at, whether anyone has already had experience with that.

But drywall walls block quite a bit. Almost not at 2.4 GHz but at 5 GHz. Are you putting them on the ceiling? How large is the "open space" on the upper floor? On the ceiling is always better due to the radiation pattern. In the worst case, just on the wall. Since you still have LAN sockets in the rooms, retrofitting is easily possible.