There really is no "slide" on the Luger, only the receiver. If you have the grip piece and the receiver, you about have the gun. But Lugers were pretty carefully fitted and building one from parts would not, IMHO, be practical in terms of proper fit, headspace, etc.
Nor would there be any advantage. Unlike the M1911, there is no industry turning out guns or parts. All the major parts are about unobtainable and prices are high when available. If one is not too demanding of condition, it is still possible to buy a Luger for around $600, and with a bit of luck get matching parts or at least parts from the same maker. Even fairly nice ones can be had for $900 if willing to take low-demand guns like the "1920 Commercial" in 7.65mm.
The Luger is a fascinating gun, and I am sure you will have fun studying it whether you build or buy.
Jim