Below are my sketches for the angel character. The aesthetic I'm going for is almost art deco in style but with soft edges. I'm also very fond of Josep Maria Subirachs' work on La Segrada Familia. The angel should be very tall (8-9ft) and very slender. The wings shouldn't be a prominent feature when at rest. The angel's arms, wings and robe should all have a complimentary vertical flow. One important feature is the headdress or cowl which is visibly a separate piece that covers the head, but it should flow into the robe. In the second sketch, I have made several variations on this headpiece, but feel free to play with this feature a bit.
The features should be minimal. The face should not have heavily defined features (cheek bones, temples, mouth lines, etc.) but they should be soft. The hands should be long but not heavily detailed either. Below my sketches are some references that I feel capture the style I'm after.
Angel Reference Gallery
Initial Concept Draft