This is a big one. You don't want to risk shocking yourself or changing the polarity of the electrical wires. You home could lose power due to a surge and some wiring issues can lead to house fires. So please be sure to contact an electrician before taking the chance.
Don't get us wrong, some plumbing issues are easy to fix on one's own, but the major issues should be checked out by a plumber. If a main pipe under a sink were to need fixed, for example, it would be best to call in professional help. No one wants pipes to burst. If a toilet is installed incorrectly, you could run into some drainage issues that lead to stoppage. Would you want to come home to some sewage issues? Neither would we.
Sometimes when adding on to your home you need a permit. It is possible for homeowners to acquire these themselves; However, it would be wise to have a professional complete this task to ensure you get all the correct permits necessary. Contractors will be able to get you the permits, be sure inspections are passed and handle the corrections to pass the inspections.
Sure, you may think tearing up carpet sounds really easy, but there's a lot more to it than what most of us would think. Not only do you have to worry about the nails and dust involved, but there's also the question of what's underneath. If the floor underneath isn't the magnificent wood floor you had hoped for but instead you find a subfloor, you would need to repair the subfloor and then install new wood flooring on top. This can be a huge unexpected cost. There is also the disposal of all unwanted material, including the carpet pad underneath. A professional would take care of this for you.
First of all, tiles are really fragile. It doesn't take much for them to crack or even completely break. There's also the issue of laying them perfectly. If they aren't laid out exactly as needed, you will find by the end that nothing is straight and appears cheap.
So please... be safe and consider hiring professionals for these important home improvements! It could prevent injury as well as extra unexpected costs.