Designing a personalized blanket?

I want to make a blanket for my step-dad’s 50th b-day
is there a website that you know of where it shows you how to create your own pattern?
I cant find what I’m looking for I found a grid-paper type sheet online where i could just color it in to see what it would look like
but i want it to be 60sts by 100 rows so I dont want to look at little boxes an try to count it on paper than by stitches :wall:

Can You Help?:pray:

What are you attempting exactly?