Ok, so you can make an obby generator using the following method. Have water run across 7 blocks with a redstone line just at the end of it. then have lava flow over the redstone and it will turn the redstone to obsidian.

Now, you can use the set up like I have, if you look at the picture below.
You'll want a dispenser hooked to a button with a bucket of lava inside. (Get lava from trading for obsidian, or use your starting lava.)


You want the water like this, I like to keep mine covered.


The redstone goes at the end right under where the dispenser will put the lava.


To help clear the lava, I have two pistons hooked to a pressure plate, but you can just use cobblestone or something. Anyway, the lava will come out of the dispenser and flow over the redstone, converting it to obsidian and then continue to convert the rest. If you put the dispenser one block up, the lava will spread farther than how I have it.