HeroScape's Master Set (Rise of the Valkyrie) includes a remarkable amount of terrain, along with 30 figures. But if you want to build an epic HeroScape battlefield, you need more than just the Master Set. Here are my suggestions on what to buy, in this order.
(1) HeroScape Master Set: Rise of the Valkyrie -- Your first purchase should definitely be the Master Set. And not just because you need it to play the game: it includes the most terrain (a total of 273 hexes), plus two ruins which can be used for cover by most figures.
(2) Road to the Forgotten Forest -- This expansion includes a bridge and road terrain, which give you a lot of flexibility when constructing battlefields. The bridge can be used to set up a central river crossing point, which can turn into a real hot spot of action. And it has five trees -- which really make your battlefield look impressive while giving the figures something to hide behind.
(3) Fortress of the Archkyrie -- I strongly recommend this castle, which is the best expansion I've ever seen for any game. Players are given a phenomenal number of customization options when building a HeroScape castle; it feels like there's no limit.
(4) HeroScape Master Set: Rise of the Valkyrie -- A second Master Set gives you another 252 land hexes, 21 more water hexes and 2 additional ruins. This is a necessary investment for serious HeroScape players. Around this point, you'll also need to buy some large plastic tubs to store all of your HeroScape terrain and figures.
(5) Volcarren Wasteland -- Lava fields, molten lava and the Obsidian Guards give you some interesting new options. Characters who end their turn in a lava field could wind up dead; any character who moves onto molten lava is almost certain to perish. This set is available exclusively at Toys R Us.
(6) Thaelenk Tundra -- This expansion features snow tiles, ice tiles, glaciers and the Dzu-Teh snow beasts. I love the way the Tundra looks on the battlefield, and the ability to create snow-covered mountains and a frozen river or lake -- all of which can take longer to move across -- is terrific.
(7) Road to the Forgotten Forest -- With another bridge, you can create a second river crossing or make your lone bridge double wide, and the roads allow figures to move more quickly across the board. The Dumutef Guards (one comes with each RttFF expansion) are interesting figures as well.
(8) Fortress of the Archkyrie -- Do I need to explain why a second castle expansion is worth buying? Best. Expansion. Ever.
(9) HeroScape Master Set: Rise of the Valkyrie -- Yes, a third Master Set. It comes in handy when you want to build a large board.
(10) Thaelenk Tundra or Volcarren Wasteland -- A second set of either of these expansions, whichever you prefer, would be my next choice. A third set of Road to the Forgotten Forest is another great option -- the road tiles and bridges really do help the HeroScape battlefields take shape.
Some enterprising HeroScape players have built custom terrain for their games; Heroscapers.com has some great tips on how to do this yourself. Custom terrain is often available for sale on eBay.
While you're building your terrain library, don't forget to add more figures as well. Most of HeroScape's character expansions also include a small amount of terrain, so buying new figures adds to your terrain library at the same time.