Since you’re building custom PCs for a client, you would need to discuss a great deal of things in terms of the level of customization that you can offer to the client according to their budget and needs.
The categories that you would need to discuss are: graphic/CAD/CAM design workstation, thin client, home theater PC, gaming PC, audio/video editing workstation, and standard thick client. These things refer to the level of specifications that each equipment would require according to how the client would use them.