Building Mechs

Is there a tutorial on how to build Mechs or where I can find the Mech items?

No tutorial, but Mech items are in the Items sidebar list. Setting the category will make the proper fields to appear.

I can´t find any Mech Items (Mech category?) in the Category list.
Where are the Mech and Vehicle sheets?

Why don´t you do it like with the ships? PC Ships, but instead PC Mechs and PC Vehicles.

PC Ships have been an issue for content development and GM alike for quite some time. They will eventually match how Mechs and Vehicles are currently handled. PC versions will be created in the partysheet with simple drag and drop from NPC records or creating them from scratch. This will help GMs and content developers as they will only need to create one record and can be used in multiple ways. This will eliminate the exporting of PC ships, but a NPC record can be made to export. This is of course a future goal. As for Mechs, Vehicles, and Drones, they can be created in the same fashion, but instead of the partysheet, they are created on the owner's character sheet. You can create a new entry by clicking the green plus button or drag and drop an NPC version of the record to the vehicle tab. Then dropping relevant components (found in items) to the record will then populate it and set the relevant fields. Vehicles still need more fleshing out and a more automated solution may be found, but it's a more manual process for that record.

I finally found the Mech Items under : Items/Type.
There are Armor, Weapons and Templates buttons on the top. Can't you just add Ships, Mechs, Drones and Vehicle buttons as well. That would make things much easier.
Btw, unter Category there is one that is called : "HeavyArmorHeavy Armor" . I assume that this is a mistake :)

Hi, for a mech created on a character sheet, how do I increase the tier of the mech? It does not look like that is editable, and dropping on frames, etc., do not seem to automatically adjust the tier? It looks like "level" is editable on vehicles, drones, which would be similar. Also the hover text says "Tier level of starship," but doesn't work the same way (that field is editable on a starship record sheet).

I also run into the issue of if I add a mech from NPC's on the character sheet, but then try to add a frame, upper/lower arms, etc, (by dragging/dropping the item), it does not apply. If I create the mech directly on the character sheet however it allows me to do so. Is that by design?

PC mechs from the PC sheet adjust their tier based on the MP you set for the mech. That is by design per your question related to NPC mech drops. Since NPC mechs are created with text and not item records it was hard to work in the automation of the component drag and drops with text. I would suggest just creating the NPC mech as a PC version if you plan on using it long term.