Here is the core of how INLGames designs this type of system for fire, flooding, fog, etc. The core concept is offloading a little pre-game work to enable a simple and fast system in play.
Make some fire markers:
* Cut strips of red construction paper (or fancy colored paper, if you want) about 1/2 the hight of the minis. Give them a jagged edge if you want.
* Glue them closed into a ring. Pick your diameter. If you want squares, flatten them and fold, then repeat and you have a square (which you can size by picking the circumfrence of the circle). Hexes (or anything – penrose tiles?), too, but the folding is a little more complex.
Pick something to show the wind direction. Ornate mini or paper arrow.
Initiate fires however your scenario says.
At the end of a round (all players have a turn), roll dice for fire progression. Roll one die for each fire token on the "leading edge" of the fire. Each fire token that succeeds for fire progression gets another token, adjacent to it in the direction the wind is blowing.
Fire Dice:
* Take a regular die, color the one and the center pip of the five red. (Note: this is not a "speical" die – it still works perfectly as a regular d6).
* Fire progression success is rolling a red pip.
Leading Edge of the fire:
* The tokens that don't have a fire token in the direction of the wind.
* Roll one die for each token on the leading edge, apply them spatially.
* Example: Wind blowing east, five tokens on leading edge. Roll five dice. The die that lands the furthest north applies too the northmost token, and so on working south.
* If the fire gets really big, do it in salvos. It's a little more in-game overhead, but its scaling to support the scope and granularity you decided was appropriate.
Dynamic Wind:
* Color the one pip of a die red and the center pip of the five green.
* After rolling for fire, roll for wind. Red = turn to port (left, based on the indicator's facing). Green = turn to starboard (right).
* You can use whatever color coding you want and whatever distribution you want. You can even mark the color code on the wind indicator.
Obviously, you don't have to go with the 1 in 3 distribution above. You can make whatever you want, even get some blank non-d6 if you want and go to town. The important factor is, one system will support many, many distributions.
For your situation, I would get black dice, green dice, and yellow dice to represent buildings, forest, and brush, and give them 1:6, 1:3, and 1:2 odds respectively. Multiple die colors for different terrain is a little more in-game overhead, but proportional to the level of granularity you want for your scenario.
You can also implement wind speed by having a wind speed roll after the wind directioni roll. Six increase (up to max), one decrease (down to min); color coding works here too. I would have little bins for the different distros on the dice based on wind speed. When wind speed changes, get the right little bin and put the current one off the board in storage.
Everything here could be converted to a table and chart method, with windspeed columns and terrain rows then a "to hit" number (I always write "equal or exceed" or "exceed" on the chart itself.) if you prefer tables. You could even do a nomogram for wind direction/speed changes.
Hope this helps.
