my two cents’:
the game’s the thing. gaming with miniatures carries a good deal of consideration for the visual appeal, but if/when the modeling gets in the way of the dice rolling you need to stop and decide whether making a cool-looking diorama is the objective rather than a playable game. so the first step is to look at the rules: how does terrain affect the game mechanics? do elevations need to be distinct for determining LOS? same with woods, towns, rough-ground and the like: do they require clear edges that display an area that represents a terrain type? how will stands/models be moved through or placed in features? what is the ground scale as it relates to movement/firing? do features that look correct with the model scale mess with the game by occupying too much space? -does movement or firing across them create problems? answering these questions (and others like them) before you start will go a long way towards saving frustration and wasted effort.
as to specific terrain: 13 years old to me = poor (at least i was!). that means getting by with maybe-not-so-professional-looking stuff—but again: the game should be fun even if you’re using miscellaneous pieces of what-not (for both the terrain and the models). if it isn’t—and you need the shiny bits to make the game work—then you need to dump the rules and get a better game. that said, a mat/cloth can be had cheaply by going to walmart (or other similarly evil big-box store) and buying a set of flannel bedsheets—they’ve got a nice olive-drab-ish one that works fine. if you can afford them, a couple rattle cans (krylon camo-colors are nice) can be used to give the thing a more varigated appearance—just remember to spray it outside!
if the rules allow “soft” hill edges, pieces of cardboard (standard corrugated box stuff—pick it up for free anywhere) can be cut and placed beneath the sheet—for 6mm scale you don’t need anything really tall. if you need/want distinct contour lines, use the cardboard but cover it with the fitted sheet that came with the set. if you want, the edges can be made better-looking (sloped) by spending time (that’s what you use when you don’t have money…) squeezing/gluing them together.
woods, rough ground, swamps, etc… requiring hard edges can be shown with pieces of the pillow cases to match the tablecloth/sheet—they can be spray-painted to look distinct and/or sprinkled with appropriate whatever—lychen is (still?) cheap, or you can make your own by shredding old pillow/packing foam and sloshing it with latex paint (had for cheap from the “oops” pile at the home stores). at that scale (6mm) i wouldn’t bother with treetrunks: big chunks of lychen/foam look fine enough from the “500’-general” POV.
towns are best done with pieces of thin cardboard (the backs of spiral notebooks work well—probably a good enough color as is, too…) to show their extent (again: depends on how the rules treat them) with a few moveable buildings—the downloadable cardstock stuff recommended is good. if your fingers won’t cooperate, grab the family’s monopoly game and paint up those! thrift stores are great places to hunt when it comes to finding pieces of this or that that will work well on the gaming table.
rivers and roads. cheap masking-tape is fine, IMO. there are enough colors on the market that look okay, and you can always do a little marker/pastel/chalk work to punch them up a bit if you so desire. plus they have the benefit of being any shape/size.
okay, i think i’ve blathered enough (probably too much…). hope this gives you some ideas.
