Leak in skylight and looking for recommendation for changing to velux.

Hi, I have an existing perspex glass skylight in my kitchen of a house I bought last year. The kitchen is a garage extension and has a flat roof. We noticed a leak recently in a period of really heavy rain through the skylight.
We are looking to replace the skylight with a velux window and was wondering if anyone could recommend a reputable builder/roofer etc who could look at this for us and install it.
Also what would the estimated cost for purchase and installation we should expect to pay. Thanks

no size of rooflight given
no indication of where you are in the country the job is
and no indication of performance expected

Rooflight is square approx 60cm x 60cm
Based in South Dublin
We expect a good job by someone reputable but at the same time don't want to be ripped off. So indication of an estimate price for purhcase of window and installation would be good along with maybe someone to advise on the source of the leak as with a flat roof I am wary that it might not just be a skylight issue. Thanks