^ Okay, don;t know what happened to my other reply from this morning... but will re-write it again...
Basically, i would first advise you trace out the inside of your 10G's footprint, then on that tracing, work out how much above water land area you want to create...
Once you have a drawing / tracing of the area you want turned into a land area, go out and get a piece of acrylic cut out in that shape... but make sure its going to be thick enough to hold up the weight of the land area... so maybe about 0.5cm or more thick...
Once you have the piece, drill lots of small holes in it, so that the water can pass through the bottom to help prevent the plants from getting water logged and rotting the roots away...
While your at the acrylic shop, you'll also need to get a few "L" shaped pieces of acrylic cut as well, this will be the support for the land area on your tank, so depending on the size of the land area you may need 3 - 4 pieces made...
If you have any other specific questions, let me know and i'll try and answer them for you...