Here's a question: Are the Fortifications (p. 114-119 in the 6th Edition Rulebook) available only to Imperial armies (Space Marines, Imperial Guard, Battle Sisters, etc.), or can they be used by any other army? It would seem unfair if only Imperial players could have access to the Icarus Lascannon and Quad-gun that are so good at defending against flyers. However, it would also be really cheesy if my Tyranid force had an Aegis Defense Line with Quad-gun, or a Fortress of Redemtion with an Icarus Lascannon.
If fortifications can actually be taken by players of any army, would it be acceptable to model a set of converted/kitbashed Tyranid-looking walls with some kind of mounted biocannon and count it as an Aegis Defense Line with Quad-gun? I already have several Tyranid bits from various kits, and several Tyranid Spore Chimneys and other Tyranid stuff from Forgeworld that I haven't done anything with yet. I could easily model a Tyranid version of an Aegis Defense Line with Quad-gun.
I would never even try to use any Imperial Fortifications with my Tyranids - It's just too cheesy and totally outside of any realistic storyline/fluff. However, if possible, I think some kind of Tyranid bio-construct wall with a mounted bio-cannon capable of shooting down flyers might be feasible from a storyline/fluff perspective (if those Fortifications really are available to all armies).
What are your thoughts on this?