My roof screws need replacing because of rust, do I do it myself or get someone and pay them ? And how much will it cost ? It's a 4 bedroom obviously tin roof.
The first question to be asked whether the whole roof needs replacing - if the screws have rusted out, what condition are the roofing sheets in? Exposed-fastener sheet-steel roofing is NOT a long-term roof like concealed fastener standing-seam. It's an inexpensive, short-life-span roof. (If it was actually tin, you'd strip it off, take it to a scrapper, and put on just about any roof you'd like with the proceeds.)
As for whether you hire it done or do it yourself, that's mostly up to you, your ability to work safely and/or equip yourself to work safely, and your willingness to pay to not be bothered, or take the time to save money. Don't scrimp on safety - falling off a roof can be fatal or very, very expensive in both money and future incapacity. If you hire someone else, make sure that they are actually insured for the work.
I have cleaned up (caulked and re-torqued, as some screws were leaking post-install and it was simpler to do them all that to try and sort exactly which ones) an exposed fastener roof of about 16 squares (1600 square feet) as a DIY job. I dropped a chunk of change on climbing gear (harness, static line, locking carabiner, rescue ascender) at the outset, and I think I replaced my failing cordless drill with a brand-spanking new one as well. It wasn't bad, but I'm not you, either. Ultimately, what you choose to do is your choice.
Y our problem is one most people experience unless the roof was installed with the new type of screws. It is not unusual to have to replace them every 10 years or sooner. you can do the job your self if you feel safe doing it. Tin roofs are very slippery unless you are wearing the proper shoes. Always carry a claw hammer with you in case you begin to slide. Should this happen to you, you take the claw hammer and drive the claw into the roof and hold on, it will save you from falling. Anyway you can do the job your self just your building supply company which screws they recommend.