Centralised wifi based system

Hello All,

I need some help on how to take signals from sensor with esp-01 attached acting as a slave. I have such 20 slaves and connect them to single master. What will be the best option of hardware and software ? Open for any type of suggestions to build on.

Slaves are ready with esp-01 mounted on it and now how to send data 1/0 to master or assign all data ro particular IP, So it can be accessed on web.