Nesting House Sparrows

I have house sparrows that nest in my roof every year - I think there are two or three nests, possibly under the eaves or behind the guttering somewhere - I haven't been up a ladder to have a good look yet! I need to replace all my windows, and also facias and guttering, so I would like some advice on how to do this with the least disruption to the sparrows, and to make sure they come back to nest next year. I know that this is the right time of year to do the work, but not sure how to proceed. Is it better to put up nest boxes to replace the nest sites, and if I did that, would the sparrows happily use them? Or should I be trying to make new holes in the facias or leave access under the eaves to the existing nests? I do want my roof to be watertight though! Any advice gratefully received: the window companies/builders have been giving me very strange looks when I say I want to keep the sparrow nests!