Oh, a heavy‑duty frame—nice! I’d start with a solid hardwood base, like oak or maple; it’s strong, resists warping, and feels reassuring under the weight of a high‑tension fabric. If you want extra stability, add a steel plate underneath or use a metal angle iron as the backbone—those hold up to the pull of a giant hoop. For the actual frame, a sturdy steel or aluminum channel gives you a crisp edge and can handle the constant tightening without loosening. Don’t forget to anchor the corners with metal L‑brackets and some rubber feet; that will keep the whole thing from shifting during a marathon stitch session. Happy building, and remember: a solid base is the secret to a perfect seam!