The Lyre will cut labor costs by half, so a 15% total discount on the fortress if we're not already using totally free labor, and we still have to pay for materials even if we're harvesting and processing them ourselves. The Stronghold Builder's Guide is weird sometimes, though I love it anyways.<br/><br/>I'd suggest Iron as the material personally. Iron and Stone are the only sturdy solid materials that can be permanently created by magic...by the book, casting Wall of Stone at CL12 is -50% to all stone components, and CL16+ is all hewn stone walls for free. Presumably that would be the same for being able to cast Wall of Iron, since the two spells create walls of identical proportions per caster level.<br/><br/>Iron is also more stylish, it can be black and have spikes and stuff.