Going further on from Crank39s post , resealing it requires certain materials and machines. I had already mentioned the ' Dessicant ' which has to go in the spacer bar , then there is the external sealant, which if handmade would be a ' hotmelt', which would require a machine and the knowledge of how to apply the sealant without making an absolute mess , or much worse , burning yourself on the homelt( which generally sits at 190 degrees c! ) and on top of that very few master how to make sealed unit very quickly. My knowledge comes from years of manufacturing sealed units using hotmelt and training employees to use it...trust me they may look simple but actually there is a fair bit of knowledge, work and materials that go into it.
If you need a new unit, as Crank39 says, just buy one , its not worth the hassle or the funds to try and make it yourself.
If you wish to know how to make a sealed unit then my advice is find a local manufacturer and ask of you can watch as they make one