Part of the motivation for this project was to get more familiar with Fusion 360 components, constraints, and parameters after seeing some great demos by Mike Tracz. Check it out here: dev2.loothgroup.com.
Almost every marker holder dimension is a parameter, but it can be customized using only 2 parameters which specify the holder width and the number of marker holes in the first (a) row. The .stls provided have marker holes sized for Mohawk Brush Tip Markers in rows a,b,and c. Row d is sized for Micron pens. Each row can be customized using parameters for a different size marker.
The spacing of the holes is staggered in alternate rows so you can see the marker color name. The last Mohawk markers I purchased have new labeling so the color name is visible at the top of the marker.
I printed mine with PLA+. I recommend using no more than 10% infill to save material and print time. I also used fuzzy skin for the outside (skin point distance=0.25mm, skin thickness=0.15mm)