Is this the design you were trying to estimate the stone for? Looks like more than 20 SF!
I think the second tier on the patio is pointless. (Nice dog by the way) It's not usable space and it's too big to be a step. I would take the extra square footage of wall block and use it to build a nice seat wall on the upper patio and do a nice set of radius steps that descend into the yard.
I also don't quite understand the walkway leading into that little wall with the concrete things on top. What is that area currently used for? It looks like it's a walkway that steps down into the yard.....why block it with a wall?
I think the plantings need more evergreen support. Hosta gives you about 4 months of show and that's it. Until the hydrangeas and hostas push, you have a pretty baron area with just the GM boxwoods. I would maybe wrap the corner with some broadleaf evergreens like Otto Luken or Pieris. Maybe wrap some helleri holly in front of the dogwood with the annuals tucked in behind.
The images as you show them are not unified to me. They seem disjointed in both style and materials, but that's partly to do with that sucky ProLandscape program you are using. (sorry that was harsh) A plan view of the overall space would show a lot more of the intended unity. Are you taking out the basketweave brick walkway area?
When do you meet the client to present the design? Hope I didn't rip it apart too much. Without criticism you'll never grow.