Grid Builder: Drag ‘n’ Drop HTML Grid Generator
Grid Builder is a web application handy for anyone looking to create a base HTML-CSS grid quickly.
On a canvas with a 3*4 grid, you simply drag 'n' drop the given grid units to create the desired template (like a 3 column design with a header and footer).
After that, just click the "Show me the code" button and get the HTML-CSS output of the designed grid.
P.S. You can also check out "The 892 unique ways to partition a 3 x 4 grid" article andget the PDF provided to find more about the 3*4 grids.