In the Custom Layout, you can turn a metric column into a bar chart with a corresponding percentage value, or a percentage value with a corresponding bar chart. The percentage value is the metric value or total for the overall non-filtered request for the period.

Create a request in Excel using the Custom Layout.
Right click the metric value column.
Select Change Output Display, then the type of microchart and percent display you would like to see.

Report Builder changes the display in the column to match your selection.