I don´t know if someone has already posted this problem, if so, I couldn´t find it, so that is why i´m doing this post.
The thing is whenever I put a lantern (mostly the wall attached ones) in the bulding design, when they start building it they won´t put them and the building will always remain unfinished.
Does anybody know a solution apart from erasing the lanterns and putting them before the building is finished?
Normally I find the hearthlings put the decoration aspects up last, if they are stalled it seems they want the carpenter to make the thing again even if there was one already in stock, a lot of times I leave off lamps until they complete the building and put them up separate.
This might be related to the following topic:
Then again, it also might be a whole different problem on its own.
There’s just something off about placing props inside/on buildings.
I assume you’ve checked for the obvious things like having the lanterns in your inventory.
An issue I’ve run into with wall mounted decorations in general is that if you have something like a chair, crate or chest blocking the section of the wall right under the wall hung decoration, it won’t be placed. If you remove the obstruction, they’ll build a ladder and mount it.
Welcome to the forum, @Shijakari 
As @Unatan2 and @Gaddiel mention, the decoration is usually placed when the rest of the building is finished.
Hearthlings might get blocked by some other object under the lamp and in that case they won’t be able to place the ladder.
Until you don’t have the lamps in your inventory (either crafted or bought) they won’t appear as a ghost to be placed in the building.
In any case, could you upload a savefile where you are running into this problem so we can take a look at it?
To upload a save, locate the folder in
C:\Program Files (x86)\Steam\steamapps\common\Stonehearth\saved_games (assuming a default Steam install), zip the individual save’s folder (not the entire saved_games folder), and upload it. If the *.zip is less than 10 MB, feel free to upload it directly to the Discourse. If larger, please upload it to a cloud storage site like Dropbox, Google Drive, File Dropper, etc. and post the sharing link here.
First of all, thank you for this quick response.
I do have the lamps in the inventory, but the thing is they never appear as a ghost, they only appear in the design. And I have a question, when you mention to upload the savefile, you are referring to the file in which the game where this problem is ocurring is saved?
Also, I don´t know if I should post this in suggestions, but Wouldn´t be recommendable to erase the decoration from the building templates that the game gives you? Because I´m using the Black Forest Inn template.
To your first question, the answer is yes.
If you want to recommend to remove the decorations, make a new topic in the #suggestions category.
Are you saying this because of this issue you’re having, or because you want to suggest it?
I think, Shijakari, the ghost of the item only appears on the building, when one of your hearthlings gets ready to place it. So it seems like it only appears on the design.
Building no lanterns is a problem, but what to do if my hearthlings build a stone door instead of a wall lantern on my castle?
Anybody else got this misplacement problem? I solved it via reloading and using the town alert, so my stupid worker dropped the door, then picked up the right lantern.
I put the files in the drive below, if you need permission to get acces just send me the mail.
https://drive.google.com/drive/folders/0B0eGbRusD9x8V08zQlk2azVjc3M?usp=sharing
As for the suggestion, i thought it would be useful so this problem doesn´t happen to other people
Your hearthlings finished the Inn fine, lamps and signs included.
I believe that the problem with your lamp in the wall, it’s because that lamp is not the wall-mounted one, just the garden one that’s meant for placing on the ground or on top of other objects. I don’t know if you could directly place it there, or if you deleted a block from below after placing it.
Definitely something to take a look. It (probably?) is a bug that you were able to place it there, since your hearthlings don’t place it even when I made ladders just in case.
Ok, I will try and check that. Thank you for your attention and quick response, you sure are a really good team and I expect great things from this game 