Greetings

For the High Elves of this world I can think of 2 concepts with a central idea.

Concept 1) In the capital and major cities, the architecture could be marble, green glass domes and gold decorations. In smaller settlements and those closest to the border, structures could be built inside large trees or in the tops of them.

Concept 2) In the capital and main settlements we could see structures like those of the Lothlorien elves, while in smaller settlements and periphery we could see something like the halls of Thrandruil in the Black Forest.

In any case, all this would be inside the forest. If they have settlements in the mountains or in open spaces or closed the sea, the main architecture would be the one exposed for the capitals of concept 1.

See you.

With a name like High Elf.  It would assume that they are a higher breed of elf indicating a lower form of elf (lore wise)

With a group like this I would imagine them being a bit stuck up.  A sense of pride and accomplishment that is rivaled by none.  Their lineage and immortality has made them feel that other races are inferior and their structures should show that.

Imagine large stone and ivory walls with intricate art and design carved into it that reflects the very nature they embrace and worship.  A central mother tree would be their capital surrounded by grand spires and beautiful structures weaved into the forest surrounding the great tree.  Lineage built into every structure based around the passion of the family who lived there.  The height of towers was a status symbol.  A large building or tower could easily be the home or establishment of someone important or rich.  The further from the mother tree you got the simpler homes would become.  Some built alongside the trees to maintain their balance or even built around the tree, carefully designed to not impede its growth using ladders or spiraling walk ways connected with bridges to keep the community closesly knitted. (I imagine a mesh of blood elf city structure in World of Warcraft tied in with land like the wood elves in everquest.  While frustrating and funny to see all the dead laying on the forest canopy as they had fallen from the area up top, it still is a great imprint on my mind from earlier years)

Ruins 

Elf army design

Normal- Full armor with 3 different class such as warrior high elf and centaur, other army is using bow and using fist

Nature itself, deserts, forests, rivers, jungle, coast, etc.

Main city  in the forest I guess. Elves getting the best of the natural environment, buildings in communion with nature. Glass, jewels, gold, silver.

Some of us already posted some pictures on the Elves race discussion, 5/5, exclusiveness, sometimes I think it's redundant or devs aren't reading.

Minor cities can be less cocky, but still elegant.