Tools for report design/planning

I don't come across many UX/UI designers around the Power BI forums, but speaking as one, I can say that I commonly create wireframes and prototypes before working with developers on building PBI Reports (we call Power BI reports "dashboards"). I work for a pretty large enterprise with UX and design teams scattered throughout the organization, but I am the entire UX team for sales, finance and analytics. I have a work process that provides that initial prototype for stakeholders to review before we actually gather data sources and build dashboards. This workflow isn't really for one-off reports, but more for enterprise-wide dashboards that many people will use (internally) for sales reporting or client revenue, etc. A lot of these dashboards are emberrded directly into salesforce pages. Back to my design process - I will typically meet with stakeholders about business requests and sort of sketch out what the request is. I then refine that sketch into a wireframe (I use Axure RP) or, more likely, a high-fidelity prototype of what I think the dashboard should look like. We then go through a few rounds of discussions with stakeholders and developers to refine the prototype until we all agree it meets everyone's needs. The advantage of the high-fidelity prototype is that it looks real, so stakeholders really understand it (wireframes and their low-fidelity can sometimes be confusing to business leaders), also when I hand it over to the developers, they know exactly how to make the PBI dashboard. I also provide specs that include colors of all the elements, font sizes, pixel spacing, etc. It's a pretty good process. As I mentioned earlier, I use a prototyping tool called Axure RP, but there are many others. One key feature (of pretty much any of these tools) is the ability to design and build a library of UI elements in the prototyping tool that mimic the power BI elements. This makes it much quicker to create new dashboard designs.