About a year ago I saw a thread on the White Flower Cake Shoppe flowers (don't remember if it was this thread...) and was fascinated with the giant flowers. I purchased a DecoPac tip 403 [these are hard to find] and made these cupcakes. I'll attempt to share the resized photos below. First pic is size comparison. Smallest tip is the Wilton tip 81, the next size (for comparison), is a Wilton 2D, and the largest tip is a DecoPac (not Wilton) tip 403.
I played around with the stiffness of my regular buttercream (will provide link to recipe below) and played around with how to create each petal. For a first time out, not too bad. You can see that it may take practice to eliminate the "bulge" at the bottom of my petals and develop the muscle memory (pressure, pull, stop pressure, release) to make these quickly and correctly.
The buttercream was sufficiently stiff to hold the shape. I ended up freezing these and gave them as gifts later.
I use a buttercream recipe provided by a Wilton forum member, Bunnywoman. BUNNYWOMAN'S CRUSTING BUTTERCREAM: (a lovely lady on Wilton.com)