Replacing Flashing At Chimney Stack

Hi;
I am renovating an old cottage & there is water entering the house through the flashing on the roof, is it a big job to replace the flashing & replaster the stack, ie would it be a DIY job or would you need a professional for this job ?
Also any idea what this would cost for a single storey cottage with a standard size chimeny stack ?

Thanks in advance

Not a major job at all but certainly not a DIY exercise either. A good joiner (or even a blocklayer) will sort you out.

Cost? No idea as it will depend on what part of the country you are in and who you get. There may be the issue of the type of masonry involved - block or brick, counter-flashings, drip tray, etc