your uncle invites you to spend the weekend with him.write a letter to accept the invetation. mention the time when you will reach his house.

Here is a sample letter for your reference:

18/201

Shivaji Nagar

New Delhi

17 June, 2011

Sector - 4

Fatehpuri

Haridwar

Hello Uncle,

How are you uncle? It was very nice to receive your letter the other day. I am very thankful to you for your offer and am pleased to inform you that I would love to join you for this weekend.

I have always wanted to go river rafting in Rishikesh. Since the day you had shifted to Haridwar, I was wishing to make this plan. I am very excited about this entire venture and have booked by tickets in Royal Cruiser. I would be reaching your place by 4am on Saturday and would return by the 11pm bus on Sunday.

This trip is highly awaited. See you soon, 

Lots of Love,

Prakash