How long it takes to create your own responsive map like google map

our propose project is a resort finder and reservation of a village...then the map we are going to use is google map...but they insist to use it...they said we need to create our own map like google map.. my question is how long it takes to create that map and also how many people we need to finish it on time (our project was needed to finish by 4 months) thanks in advance