Okay, Ariana05, here's an answer that will probably help out a lot:
Option 1: insist that the AutoCAD folks you send your translated files to do the block creation...
Option 2: the Unify command is in ArchiCAD, under the Edit menu, Reshape commands. I don't use it very often, maybe I ought to....
Option 3: you convert ArchiCAD-drawn elements into GDL objects like this: once you have drawn your basic tile for your pattern (I'm assuming 2D lines, arcs, etc), select all those objects in the tile-unit-thing. Then go to File > Libraries and Objects > Save Selection As, choose a logical location in the object library file tree, give your new GDL object (.gsm file extension) a cool name, and then click OK. So now, instead of dragging multiple copies of your grouped objects, access and place your new GDL object via the Object Tool (chair icon), find your object in the file tree on the left of the dialog box that appears, and then start placing it on the drawing. It's important to note that you will only be able to snap future objects to the hotspots on the GDL object, not to endpoints etc of the lines and arcs that compose your GDL object. Try it out and see.
So, when you translate your drawing to AutoCAD, set the Save Options to "Convert complex objects to Blocks" and the GDL object will be a block in the translated .dwg file. Your recipients can then edit the blocks as needed with the AutoCAD REFEDIT command.
Try that out and let me know if it works okay for you.
buena suerte
Zolli