If it must resemble chalkboard drawing, it surely is easiest to make in Photoshop.
See this discussion about watching distances, needed printing resolutions and what image pixel resolution is needed to utilize the available printing resolution.
What resolution should a large format artwork for print be?
The printer surely tells how many pixels he can print per inch in such sizes. Actually printing resolution isn't pixels per inch, but lines per inch. He converts the lines per inch for you to pixels per inch with some marginal to get from you some extra sharpness to be lost in the printing process.
Let's assume he wants 50 px/inch to make as sharp prints as he can. Then a six feet wide image seen at distance = six feet will look out as sharp as an one foot wide image seen at distance = 1 ft and printed using 300 pixels per inch. It's scaled proportionally.
A 6 ft wide image at 50 px/inch resolution must be in Photoshop 6*12*50 = 3600 pixels wide. That's not impossible, today high resolution photos have much more.
Be sure you see beforehand a sample of what quality the printer produces bitmap images in that size and negotiate all needed details. If they do not want to guide you in technical details, walk to elsewhere.
NOTE: The drawing must be created in the needed final pixel dimensions. Enlargening a low resolution image is possible with special image resizing software, but it still is worse than having the right resolution in the beginning. Enlargening for ex. to 500% pixel dimensions in Photoshop only creates a mess.
Here's your sliced cow enlargened only to show what kind of effect special enlargening software create:
Words Fore and Brisket needed manual fixing due the unsharpness of the original