Hang on, the premise of the question is, in part, wrong. The Germans certainly had ideas about lebensraum long before WW2, long before WW1 even. These ideas certainly helped shape the German goals in WW1. Very broadly speaking, Germany wanted to become the preeminent power in continental Europe. We can break this down into a few key objectives detailed in the so called Septemberprogramm of 1914.

In the west Germany wanted to reach a quick military defeat of France, the other serious contender for continental european power, so they could impose terms that would seriously weaken them. These terms included reparations to germany, a partial demilitarization of northern France, surrendering territories of strategic importance in northern France (namely the iron-rich mining regions in Alsace-Lorraine/Elsaß-Lothringen and parts of the northern coast). Germany also wanted to either vassalize or annex Belgium and Luxembourg. This would effectively surround the Netherlands and while the Septemberprogramm does not call for military action against it they certainly wanted to make it heavily dependent on Germany.

In the East they wanted to weaken the Russian Empire by forcing them to release a series of "buffer states", basically modern day Poland, Lithuania, the Baltic states and the Ukraine. These were to become more or less vassals of Germany. These goals would enable a continuation of the centuries old Ostsiedlung, basically the settling of land in eastern Europe by German-speaking people.

In the colonies Germany wanted France and Belgium to hand over African territory which would enable Germany to create a continuous colony from German South West Africa to German East Africa.

In more general terms these policies were meant to create a Germany which completely dominated continental Europe and which would be surrounded either by vassal states or states alinged with Germany.

These were, broadly speaking, the German goals at the start of WW1.