Greenfinch

Hi, I have been a member of the rspb for a couple of years now but I really don’t know much about birds, I seem to have gained a pair of green finches in the last couple of weeks in my garden since the fruit on my mulberry tree has ripened, but they seem to have taken up residence in another tree and nest building/repairing, it seem strange they would be doing this in July, I wondered if anyone had any thoughts as to what was going on?