DWG/DFX plans snapping and modeling I have been using 3ds max as my main program for archviz. Due to a change in workplace I no longer have access to a licence and have been looking for a free alternative and found blender. 

My usual workflow in 3ds max was to import plans in either DWG/DFX format, I would then trace the walls using 2d snapping with splines and extrude the splines to create the walls.

Is this workflow possible in blender or would I have to use boxes and move the vertices in edit mode to fit the plans?
A variation of that should be possible, certainly.

DXF import was a bit sketchy last time I tried. You may need to export in DXF R14 format or something relatively old like that. FBX is more reliable.

You can certainly snap to vertices of the imported file. You'll probably add a dummy mesh (e.g. a plane), enter edit mode, then repeatedly press 'e' to extrude vertices along the background (imported) mesh/lines.

Alternatively you can just select vertices from the import mesh and extrude them. Might want to separate them from the original mesh to suit your workflow. Just press 'p' when you've selected a bunch of vertices that you want to turn into a new object.

Personally I prefer place walls as a single line along the wall centrelines and extrude vertically. Then you can adjust wall thickness easily using a Solidify modifier and you have fewer vertices to contend with, which makes cutting holes for doors and windows easier.