Roof light / glazing

[HLM0000]

hello, We are having an extension built and I need to make a decision on the glazing for the large rooflight (2500 x 1000). Because of cost, I am very tempted to go for double glazing, but I am wondering if triple glazing is worth the extra money in term of noise reduction (ie: when heavy rain). Also, would a self cleaning glass on a flat fixed rooflight make a difference?
Many thanks for your feedback :-)

[snailsontour]

We've just had a load of velux fitted and went for the double glazed but with the special coating on that stays clean and reduces the noise - was cheaper than the triple glazed option.