Okay, so when I game I usually use a big flexible battlemat which I've had for years. It's got a square grid on one side and a hex grid on the other and you draw on it with markers. But in my current campaign my players are diving into a series of dangerous challenges set by the mysteriously-disappeared demon ruler of a demi-plane. They're doing a big outdoor challenge battle right now but when (if) they get past than then they go down into more of a dungeon setting with a series of danger rooms. So I decided that for these rooms I'd do a minor bit of drawing and crafting to make them more memorable. Below is discussion and photos of making the boards. When (if) they survive the rooms I'll do a follow-up post with full pics and the rules mechanics for each room.
1. I started with two 20" by 30" foam core poster boards from the craft store, the type with a rough paper surface you can draw on rather than the shiny finish.
2. Since I wanted a grid, I started by drawing registration marks around the edge ever inch. After I finished the first board using a ruler, I marked the other boards by matching them up next to it and duplicating the marks.
3. Then I used the edge of one board as a straight edge to quickly draw some light pencil lines from mark to mark in one direction...
...and then mark to mark in the other direction to make the grid...
...which went pretty quickly.
(Also, I did grids on both sides of both boards to make them double-sided to save money.)
4. Then I used a regular felt tip pen to draw the walls and some triangular marks to show the center of each edge in an interesting way.
5. I colored in the triangles using Sharpie brush-tip permanent markers...
...and the entrance alcoves with pencil shading.
6. Finally, and this took pretty long, I used hatching and dots (based on the map style of Dyson Logos) to add some thickness to the walls. Then some Chinese characters with the brush Sharpies to indicate the dominant element of the room.