When it comes to flying a multirotor there is much that goes into it, never mind the flight operational side of things, just getting one off the ground is an education on its own. When you start thinking am I going to build one of these myself, I think its a good decision because by the time you are done you will have so much more knowledge on how the copter works.
Never mind the amount of money you can save, but when things do not look right, most cases you will have a much better approach to debugging it, right to the point where you will most likely figure it out and replace the component.

Another point with this thought is unlike the person who buys one off the shelf and gets upset with the maker, probably for no real good reason other then sometimes these things can have issues.

Most importantly if you do make your desition to build a copter, figure out what application the copter is going to serve, what equipment you would like it to have, and look at the equipments weight.

Example when I decided to build my t810 my goal was to make a copter that would be rigid, strong, and light weight, knowing I was going to be on the move with it a lot I wanted it to have the ability to collapse and fit into all our vehicles (unlike my production copter). I also wanted it to be way over powered so if you have a motor outage I knew the others would not have any issues keeping it a float.

Another key element for me was to be able to add flight time, so when the time came to building the copter, I already had a good understanding of the copter’s total take off weight, thrust capacity which allowed me to have a decent idea of lift capabilities and flight time.

When you are building these copters I believe you can break it down to 6 components and its best to have some understanding of each sector. If you do that then you will end up with a good result.
(Note I feel if you do take on a build then I would highly suggest, since you will be saving some decent money, spend a little extra for quality, it will make a difference.)

If I break it down the components are.

Fight Controller

Going forward Over the next week will put together a post of each component and quick explanation on to approach each. Keep a look out for them.

Best to all for now