You want to build, but there is no designer running a job for you?
You can participate in a plotbuild then. A lot of the smaller structures at the main map like normal houses and trees are built by Adventurers during plotbuilds. They are not contests, after beeing checked and approved by a project designer every build will be copied to the main map. If your build is not approved the designer will place signs indicating what you should improve.
How to participate in a plotbuild?
First you have to read the rules and the building guide for the plotbuild. You will (hopefully) find a list of all open plotbuilds in this post with a link to these guides. Choose a plotbuild, click at the link and read the guide carefully. You will get informations how to warp to the plotbuild and how to claim a plot (usually by placing a sign with your name on it). And of course you will find out what to build and how it should look like, you have to follow the given style or your build will not be copied to the main map.
About plotworld
You are able to break and place blocks everywhere in plotworld BUT you are not allowed to break and place blocks outside a plot you claimed. If you do so it will be considered griefing and you will get
oathbreaker rank or even be banned from the server. To teleport to plotworld type in chat "/mvtp plotworld" you can then warp to the plotbuild location. To teleport back to the main map type "/mvtp world".