Google map and custom geo fencing

I need a page for my app that allows users to create custom geofencing. the user should be able to create a custom polygon or select a circle or square. My idea is have a map stacked with a layer for the custom shapes the user can zoom in and out of the map to set location and points would have to be converted based on the pixel to location position ratios. each geo fence would be added to firestore with a title and tagged users, if the users leave the tagged location for longer that 5 mins a push notification would be triggered
see attached for what i have so far