Dump some sand in a pile on a flat surface. Work the sand into a mound or dome-like shape. Smooth the edges of the sand mound with your hands. This will help form a dip in the center of the birdbath to hold the water.
Cover the mound with plastic wrap. Put some sand on the corners of the wrap to hold it down. Smooth out the wrap to eliminate any large wrinkles.
Find a leaf large enough to cover the mound. Place the leaf upside down on top of the plastic wrap. Adjust the leaf as desired. Gently pat down the leaf, leaving no gap between the plastic wrap and the leaf.
Mix a batch of concrete in a plastic bucket following the manufacturer's instructions carefully. Use a stirring stick to get the concrete at the proper consistency. The concrete should be thin enough to mold and move around, but thick enough so that it will not run off the leaf.
Pile a large amount of the mixed concrete on top of the leaf. Cover the entire leaf in concrete, including the edges. Try not to wear the concrete down so thin that you can see the leaf. Add more concrete to the leaf if needed. Continue adding and smoothing out the concrete until the layer of concrete measures 3/4 inch in the center of the leaf, and tapers out to 1/4 inch at the edges.
Place a cardboard ring in the center of the leaf, where the concrete is the thickest. Place handfuls of concrete around the edges of the ring. Smooth down the handfuls to create a lip around the ring. This will allow the birdbath to sit on a pedestal.
Let the concrete leaf dry completely.
Pick up the leaf slowly and turn it upside down. Be extremely careful not to break the concrete when turning the leaf over. Gently peel the leaf off the concrete. Use a stiff-bristled brush to get off hard-to-remove pieces. The leaf should have imprinted on the concrete, giving the birdbath its leaf appearance. Remove the cardboard ring on the bottom of the bath. Allow the concrete to cure for about a week before handling.
Paint the concrete with concrete paint of any color. Allow the paint to dry, then apply a concrete sealer to prevent the paint from chipping off. Allow the sealer to dry.
Place the birdbath on a pedestal in your lawn or garden. Fill the dip in the center of the birdbath with water.