Well, truthfully, actually making silk plants isn't easy. And the silk from shirts is not exactly the type of silk we need to use.
I submit the following:
You can go to your local home improvement store and look in the fake plants section. Look for silk plants that can be bought seperately for arrangements. Take care not to use the ones with fake waterdrips on them. Goodwill shops usually have a few of these.
Anyway, you can either use the plants and stems as-is, or you can strip the leaves from the plastic stems and re-arrange it with the leaves, and the amount that you prefer. If you go this route, use either aquarium sealant or superglue to re-attach the leaves to the stems.
Or you can take these silk plants and cut them into different sizes/lengths. You can then take these twigs of leaves and glue them to rocks like granite and river rocks. Or, you can use a small cup or bowl (dome shaped slurpee lids work awesome) to make a mound of gravel held together with aquarium sealant. While the mound is still fresh and not dry, you can shove the stems of the twigs into it.
All in all, your limit is your imagination. Just be sure to use non-toxic substances. Aquarium sealant and/or superglue should be the glues. The plants should only be made from plastic or silk. The gravel should be either granite, river rock, or aquarium gravel. and you should be well and sure that it is completely dry and cured before adding to the aquarium.
So, just start collecting some of the stuff you need. Be patient and after a while, you will have all you need......
If you have any questions, ask away!
Paul