“rent my roof” for a new wireless start up in my area.

Looks suspicious already

​

they are installing an antenna on my roof and it will be hardwired to my router…

It smells not very good

​

.they have assured me that my personal network would be at no risk

If they are wired their access point (I suppose this “antenna” is one) to a LAN port of your router, I am suspecting you are exposing all your network to the wireless network this access point creates.