Need help with rain water harvesting (RWH) in Ghaziabad, Uttar Pradesh - How can I avoid wastage of water from the first rain?

Sir/Madam,

We are settled in Indirapuram in Ghaziabad district of Uttar Pradesh. I have a rooftop of around 1200sqft. I want to harvest rain water for which I have got 4" PVC pipe bored upto 80 feet depth and have constructed a 2'x 2'x2' tank around it. I have not yet cut the pipe to the bottom of the tank. I want to know how to go further.

Will putting a filter and cutting the pipe at the bottom of the tank serve the purpose or some other techniques to filter the water will be required? How can I avoid discharge of water from the first rain in to the ground? Please guide me. I will be grateful for this act of kindness.