Hi You say tiles, are the really tiles or slates ? tiles are far easier to replace than slates, if it is tiles they simply clip onto battens,slates have to be fixed properly or a lead strip pushed under slate which then hooks onto slate above you then bend lead strip up to hold slate in place, of course if you want to bodge it you can refix them with a dob of mastic, as for the ridge tile, that will need a roofer unless you know somebody confident enough to go up onto the roof, but then again you MUST use a proper roofing ladder, ot should not be a great expense, if you get a roofer he would clear out the gutters for you. good luck, Ray
If anybody that you call tells you the whole roof needs re-doing call somebody else out, most of us in the building trade are honest but a few aren't so be careful