Dataview for billing

What I’m trying to do

I work as a freelancer and want to create billing information from meeting notes and Design progress notes I create in Obsidian.
The structure is as following

Project/Meetings/

  • 23-09-01 Project Meeting
  • 23-09-08 Project Meeting
  • 23-09-15 Project Meeting

Project/Design/

  • 23-09-02 Project Design
  • 23-09-09 Project Design
  • 23-09-16 Project Design

Project/

  • Billing

Each note has Properties
start(date), end(date), billed(check), tags(“meeting” or “design”)

in “Billing” i have created some tables

 ## Not Billed
 ### Meetings
 ```dataview
 TABLE end - start AS duration
 FROM "project/Meetings"
 WHERE billed = false
 ```
 ### Design
 ```dataview
 TABLE end - start AS duration
 FROM "project/Design"
 WHERE billed = false
```

First thing i want to achieve is adding a total hours row at the bottom of each table
Then I’m planning to have property fields in the billing note like “hourly rate meetings” and “hourly rate design” and calculate prices from that.

The final goal would be to have a second note that resembles a bill to the customer, that i can export as a pdf file and to be able to check all the billed items with one click.

Things I have tried

I have tried to modify some of the tips here, but i think handling type “duration” is a bit different.