If you want to use hair extensions, there are two ways to find the extensions, one is buy the hair extensions pre- made before your order, in this case, and the extensions are in the general size or weight to meet the demands of most of people.
For fashion purpose, it is ok to buy hair extensions pre made since the styles and colours are usually made to follow the trend, and which could accept by most of people.
For hair loss purpose, most hair loss professional may not recommend the pre made hair extensions to the hair loss customers, for some pre made hair extensions are use clips or glue, which is not so good for hair loss, because since it just last for a few days, but it may hurt the hair existed, and it may also lead to more hair loss, especially if it being applied in incorrect ways by unprofessional people.
Another way to order hair extensions is that setting custom orders. It is a excellent choice for most of people no matter of the purpose for fashion or purpose for hair loss, for it could match your hair colour, hair textures, density, length and styles well, it also could choose the right applying ways if needed.
If you do not care too much about the price, you can choose the way that is sewn in, in that way each strand of hair need to sewn in to the existing hair one strand by one strand each time, which could create the effect of looking like your own hair.
For some kind of hair extensions it could be undetectable and could long last for several years if with the right way to care. While some hair extensions, it may need to removed and attached every few months. All these depend on the way how they are applied.
Before you set the order, you need to think according to your hair condition or the effect you want to reach, no matter buy the pre made hair extensions or set the customer order, the way which could meet your demands is the most important, and remember that the custom order need you to have patient time to wait for the hair extensions finished.