If you need chimney repair and it is beyond the point of repair for chimney tuckpointing it must be tore down and rebuilt, and there are a few things that you must do to ensure that your new chimney will last for years to come. The first thing you must do is select the proper building materials. You should use a brick that is solid with no holes in it this will increase its durability. Bricks that are cored (with holes) tend to have a much shorter life because moisture can build up in the hole cavities and break down the brick and mortar joints from the inside out, this is especially a problem in colder regions. So be sure to pick out a solid brick if you can. Next the chimney needs to be tore down. You first must protect your roof from falling debris, do this by placing a cloth tarp down over it around the chimney. You should really use cloth tarps because plastic vinyl ones can be slippery and you dont want to slip and fall, it could result in serious injury or death. After your tarps are in place start by removing the concrete cap first, the concrete cap must be first or you risk a avalanche of heavy masonry units falling all over the place and possibly through your roof. You may have to use a partner saw to cut it in sections first before picking it up, they can be very heavy. Next thing after the concrete cap has been removed is to start removing brick. It is best to use a small hammer drill for this with a pick attatchment on it and just focus the pick on the joint below the brick you are removing till it breaks free and you can grab it. Depending on the roof pitch and placement of the chimney you should use a bucket to put debris in or if you are confident it is safe below you can throw the brick down to the gound in a designated roped off area below. Be sure to remove the center clay flu liner if there is one, as well as you work your way down, but try not to break it, odds are you will send debris down your chimney shaft which is not a good thing and it will have to then be cleaned out. The brick should be removed down to just inside your roof line unless its really bad you may have to reach down further or do a little work inside the attic to get it to a secure rebuild point. Now that your ready to rebuild be get your new building materials up to your work station and start laying in brick. it is very important to keep the courses level and plum to ensure a good looking and lasting chimney. If you are using clay flue liners put one in place as you go, once it is secured by brick all the way around it up to the top then place your next one in place and continue the process till you hit your desired height. code for most areas is 10 foot from nearest roof line and then 2 foot above that for proper drafting of fumes, Generally in most cases if you build it to the same height it was you should be ok, but be sure to check your area code just to be sure. After all your brick and flu liners are in place you need to pour a concrete cap, this is one on the most important features of your chimney and it should be done correctly to ensure a long lasting chimney. Yor flu liner should be sitting about 6 inches above your last course of brick, next build a form out of 24s around the top course of brick, fill your form up with concrete till you reach the top of your form, Put a slight slope on the cap from the liner down to the edge of form for good water shedding. Also tap your form lightly as you fill it to help reduce bubbles in the pour. After it sets up for a bit say a few hours pull the form and smooth off the edges of it with a small concrete float to seal all holes and to also make the cap look nice. After that is complete install a draft cap, or also called a bird cap to finish off the chimney. One of these is needed to reduce the chance of back drafts pushing fumes back into your house and they also serve to rain out and to keeps small animals out as well. They can be picked up at just about any home improvement store and are relatively cheap. You must also install your flashing around the base of chimney as well to ensure that is is sealed and water tight.