In our company daily work we face many challenges in large modern and old buildings.
We have surveyed some of the top London Iconic buildings.
More recently we have faced the issue of concrete basements on -2 or even -4 below the 0 level(Ground).These have no wifi or cellular signal allowed by the companies in question.
You will need to physically situate your sensors at the lowest level and work backwards with the selected gateway. Ideally the gateway would be on Ground. But it is likely you will not penetrate more than -1.
We use Laird Gateways and have resisted looking at cheap gateways.
In some clients buildings we use a daisychain approach sensor to sensor mesh to get to up the Ground level. Then than data can be backhauled to the data server. Often using an alternative 868Mz RF but not LoRa.
We are always willing to try any other configuration with LoRa sensors - but the sub 0 level is always a challenge on most RF protocols.