To buy loose diamonds is probably one of the best ways of buying diamonds. There is a bigger variety of diamonds available this way and even a better price can be available as well. You can have the diamonds properly appraised, graded and valued.
Then you need to have them set as jewelry. This would depend on a number of factors, what sort of jewelry, a ring, necklace or bracelet perhaps. The type of setting, white or yellow gold or perhaps platinum. How the stones are going to be set, which might depend on the type of diamonds.
A princess cut is a square cut and, provided the stones are all of the same size and cut, If the stones are round then you might like a different setting. Perhaps you have one or several larger stones or one large and several smaller. What type of setting, claw to hold each diamond or a cement setting. A claw, although more expensive, is a better setting as the back of the stone is left open and this allows more light in and gives a better sparkle.
All these factors need to be taken into consideration.
You would need to find a good quality jeweler who can set the stones for you. It is rather like having clothes individual tailored for you. It may require several visits to check on how the setting is progressing and how it looks.
Each stone should have a certificate of appraisal that establishes the grading of the stone. The stones should be value and insured also. It is a lot more work than simply buying a present stone or stones. But when done the finish is very individualistic to you and there will be no other settings or copies the same.
To buy loose diamonds is almost what you might call the connoisseur activity of diamonds and, done right, can result in a fantastic and very individual diamond piece.