Well you may want some really large graph paper to do it with.
There is this at Amazon.com Locally you may try to find a office supply place that sells drafting supplies. Somewhere they will have a rack that hold their large format papers. You want to look for a smaller shop as the big box office stores do not generally stock this stuff.
If you search around you can go up to 27 by 34.
I also recommend looking at Computation Books they are 9.25 by 11.75. The graph paper versions are generally 4 spi. Each page is numbered and there are blank flyleafs you can write on. (like a table of contents) I have one that still good after 25 years that has the majority of my old dungeons in it. It has a heavy cardstock cover which makes it durable.
This is the brand of the one that I had for 25 years.
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