Hi I booked an apartment 3 years back. Due to the slow pace of construction , i want to cancel my booking unit. Could you please advice me on below queries,

1. which point should I include in the cancellation  application ?
2. Give me a proper cancellation application format.
3. How would I take the acknowledge form the builder.

For your information- I booked the flat in 2011. I paid around 12 lacs(7.5 from home loan + own contribution 4.5 lacs).