Since R31 all Blueprints are now for free, can be claimed in the "Blueprint Tab" next to the crafting-tab and inventory-tab. Blueprints merely require specific blocks to be in your inventory so you can claim them and then craft the Corner Stone to begin with.
There is also an option to buy all the default blocks you'll need for the completion of the respective building/structure in a "kit" with coins (to be bought with real money in the Store). Mind that the kit will always only contain the standard blocks suggested with the Blueprint. Kits will not change their contents according to your own customizations of Blueprints.
Basic information Edit
Buildings made from Blueprints currently have no special features. They are not "indestructible" nor inaccessible for other players. If you complete Blueprints "correctly" (even in customized variations) you will merely be "rewarded" by a colorful firework going off. Blueprints are still designed mainly to suggest where to place blocks as they are designed to make building large structures together with friends an easy activity.
Blueprints will not build themselves by being "filled" with the correct materials. You have to activate the cornerstones after placing them into the gameworld, and then you will be shown floating small blocks suggesting where to place the according blocks that you have collected and/or crafted.
After placing the cornerstone you can change the suggestion of blocks by dragging whatever blocks you wish from your inventory over the icons in the Blueprint - afterwards these defined blocks will be shown as small ghostly floating blocks instead of the standard suggestions.
You can additionally freely change the design of the house that you are actually building in the gameworld in all sorts of way.
Buying Kits Edit
Below each Blueprint you will get the option to buy the according Kit of blocks needed to build this Blueprint in the standard version: "Get Kit & Build Now".
When buying a kit, you will also receive the Cornerstone for free without having to collect the materials for it. So no need to claim the Blueprint itself a second time.
Again please note that the purchasable kits will always only contain the "standard" blocks that are listed with the Blueprint ("built using XXX blocks"). The kits will not change their contents to fit your own customizations.
You will need 1 empty slot in your inventory or in your quick bar when buying one kit. And another empty slot for the Cornerstone/Blueprint. The Kit will contain all the blocks needed to build the whole structure - meaning many thousands of blocks in some cases.
After buying it, the kit will at first be an icon in your inventory/quickbar looking like a stack of wooden crates. It can then be placed into the world like any common storage chest.
After the kit has been placed, it will look like a stack of wooden crates the size of two blocks in height. You can interact with this kit ("f" as the default key or right mouse button) and open it like you would open any storage chest.
You can take just as many blocks as you want from the kit and use them to build step by step. You cannot put anything back into the kit though, and after you've taken all the blocks, the stack of crates will vanish, not leaving anything behind, and you will not receive any crates in the end.
You can always pick up the whole kit with all blocks in it that it still contains, the kit will then only use up 1 slot of your inventory or quick bar. If you've encountered problems with vanishing blocks (usually they aren't loaded correctly from the server in some cases) in your gameworld it might be a good idea to pick up the kit into your inventory before logging out just to be on the safe side, as there have been issues with kits a while ago.
Claiming Blueprints Edit
Blueprints are building plans that you can find in the Blueprints tab next to "craft"-tab and "bag"-tab if you either open your inventory ("e" as the default key) or crafting menu ("q" as the default key).
You can claim any Blueprint in any number in every gameworld for free (however mind that you cannot build anything on claims of other players or in gameworlds of other players if the owners have set you to "visitor").
The Janky House (used for some examples on this page) currently is not included in the list of Blueprints, neither is the Stilt House (as of August 2016), nor the Modern House. The Janky House was a free starting blueprint for new players provided to everyone at the start in every gameworld between update R24 and update R27.
To use it, you have to "claim" Blueprints that you have in your gameworlds at first. Click on the icon and click on "claim" to do so.
After claiming the Blueprint, the icon you get will change just a little into a Cornerstone. You will need to craft this to start building the Blueprint. You should place the Cornerstone into the world then.
Placing the cornerstone Edit
The cornerstone, looking a lot like the Blueprint itself has to be placed from your inventory into the game-world (using the quick-bar) before you can actually build the house or structure. Since R26 it will now send a blue beacon-beam into the sky to make it easier for you to find it and return to it.
By interacting with it (right-click or "f" as the default key) this cornerstone will then show you the blue outlines of the planned house, so you can see how it will fit onto the ground.
You can take the cornerstone and place it somewhere else and/or turn it (use rotation by "r" or place the cornerstone while looking at the same spot from a different angle) until you're satisfied.
You might want to remove all blocks or things (like mushrooms, shrubs, rimecones etc.) on the ground that overlay with the blueprint, so that building-blocks can then be placed there instead.
Changing materials and tracking materials Edit
Once you've chosen and cleared up an area that you deem fitting, please right-click the cornerstone. In the window that will pop up you can see what kinds of blocks, materials and/or items will be suggested for this building.
You can change the list to your liking by dragging alternative blocks from your inventory over the respective icons of the materials that you want to have exchanged.
There's also a "track-"function that you can use to see the required materials on your screen while you go gather them (just like you can use for crafting recipes).
Activating the cornerstone and building the structure Edit
When you're done collecting and changing materials, activate the cornerstone. First right-click the cornerstone or interact with it using the "f"-key (default key setting), then click on the orange button "Activate".
With that the cornerstone will start to glow and small ghostly block-suggestions will start floating next to the cornerstone - they indicate where you should put which block/material to build this house following the Blueprint.
Now you have to actually build the house/temple etc. by replacing the ghostly suggestions with real blocks.
Whenever you fill in one more block, more ghostly suggestions of blocks close to the new one will start to show up, so in time you will be shown the whole building bit by bit.
Completing the Blueprint Edit
You don't have to fill in everything 100% correctly, as the blueprint is just a "suggestion". Blueprint are designed as a help for friends building large structures together. So you can use any Blueprint as merely an inspiration and change it however you like, skip some blocks, add others somewhere else, etc. The only "reward" for completing a Blueprint would be a firework at the moment of completion going off directly above the completed structure/building.
Once you're satisfied, no matter if the Blueprint has been "completed" or not, just click on the cornerstone again to deactivate it and then take the cornerstone up. You can then put it into your storage and you can of course reuse it as often as you wish in that same world where you have claimed the blueprint.
As of R31, Blueprint "prices" are free and will only require materials to craft an individual cornerstone
Available Blueprints Edit
Temporarily Removed Blueprints (since R23 and R31) Edit