Construction
If you want something built in Horizons, you have to do it with your own two hands! There are a wide selection of buildings you can set up on your own plot, or you can help rebuilt various community structures such as bridges, tunnels, crafting stations and more. Not just anyone can build though - you will need to join a Construction Class first. You can be a Mason, Fitter, Weaver, Carpenter, or Enchanter. Each of these classes has a prerequisite to join though - you will need 150 of the skill required to convert raw material into its processed form, such as essence shaping or stoneworking. Chances are that your own main class offers at least one of these skills, but if you would rather be a pure construction worker, you can take 15 levels in either Gatherer or Miner.
Once you are a member of your chosen class, it's time to get to work! Each class can produce two different types of construction materials per tier, one starting at 1 skill and the other at 100. Level 1 materials are called Construction Blocks, Sheets, Bolts, Timbers, and Spheres, respectively. Level 100 materials are Construction Keystones, Joints, Tapestries, Braces, and Sources. These repeat every tier, so you progress from Cedar Timbers to Cedar Braces to Elm Timbers. Level 1 items require from 30 to 15 units of processed material and level 100 items require 40 to 20. Once you have a full load of construction material, you can now contribute to the structure. Depending on your skill, it will take between 2 and 5 construction items to equal one unit on the structure. Also, Weavers and Fitters can make structures out of silver and leather, but no buildings are yet available that use those two construction types.
Here's a useful strategy - if you are building near a town with functional machines and you are presently doing level 1 construction, bring processed materials instead of completed construction material. If you are efficient (or close to being efficient) in making construction materials, you will be able to carry more if you create the construction materials on site. 15 units of processed materials at 8 units each weights 120 units, while a single construciton material weighs 150 units - a savings of 30 units! Be careful though - do not turn all of your resources into construction material at once, or you will be overburdened! This strategy only works for level 1 materials and only if you are building in a place that has the right machines. Selen, for instance, does not yet have a stoneworking pedestal, so I am forced to carry completed blocks.
Here's a listing of what is required for each building that can be added to a plot at the moment. Gnomish, Elven, Half-Giant, Satyr, and Dragon buildings are not yet available.