Are there special rules for crafting? The adventure "The long arm of the Hutt" says in the cargo hold of the Krayt Fang are enough parts that a skilled mechanic could build an astromech from it, but the characters don't habe the time or the skills to do so at the moment.

Of course the ewok technician in our group was like "I want to build that droid!" Now I wonder, how long does it take and what check difficulties would he have to roll against?

If there are no special rules about that, I woul let him do some maximum difficulty checks until he manages to get some blueprints or other form of data, maybe a scrap astromech he could inspect and then set the time frame to 2-3 weeks, with good rolls decreasing the time (and bad rolls increasing)

Rules for crafting droids like an astromech were introduced in Special Modifications (page 80) which also introduced rules for crafting weapons and gadgets. There have been a few other books with crafting rules including Keeping the Peace and Endless Vigil from FAD which include armour and lightsaber/podracer crafting rules respectively, there is also Fully Operational, the upcoming AOR book which will introduce ship crafting rules.

To give you a bit of an idea on how it works for an astromech there are two stages; first building the chassis which if you have the parts (specialist chassis) is a daunting (4) mechanics check and takes 56 hours of crafting with successes decreasing time by 2 hours and advantages or threats giving a variety of positive or negative effects, secondly you have to program the droid which for an astromech is navigation directives which is a hard (3) computers check and takes 72 hours with success, advantage threat working the same as before.

Of course you do not have to follow this directly and to get the full details you are best to buy the book (it is a good one) but hopefully this gives you an idea on how it works.

Thanks a lot. Will think about buying that book. Sadly the german versions are way behind and I want to avoid mixing languages or bend up having the books in english and german in the end..

Will buy the german version in any case, but I think that will be available 2018+

There are two ways to look at it. Since the craft rules had not come out yet you can just do what the book says and allow somwone to make a mechanics check and provide the appropriate rarity. Or you can let someone use the droid crafting rules, assume that all of the parts are available. I recommend the first since the description sounds like all of the parts/droid have already been built and it's been disassembled for shipping.

The adventure says something like "in cargo hold 3 you find droid parts, enough that a skilled mechanic with enough time could build an astromech droid from it or otherwise sell them for 2000 credits"

The idea of needing a proper blueprint would add a nice opportunity for a side quest (gathering the blueprints)

Maybe the programming could be also a daunting check, or come with a lot of setback dice, along with having the option to hack an imperial computer to copy an existing version of astromech programming. Maybe the code would need slight adjustments (a greatly easier computers check), but the code would have a few bonuses for the downside of having obligation with the empire..

The thing is, they already took R5-K2 from the beginner adventure "Escape from Mos Shuuta"with them, I really don't want it to make so easy to get yet another droid

Extrapolating from Special Modifications, building the CRB stock astromech would require Mechanics (PPP) to (PPPP) and 2 to 3 days for the chassis;

programming the directives might take 5? days for Computers (PPPP), I'd say.

I have modified the story a little bit at this point as the whole setting haven't really made any sense.

1) The parts worth only 2k while a rebuilt astromech is 8k?

2) The ship is capable for hyperspace jump, but nobody can make the astrogation check?

So I ruled the parts are there and some wonky way the astromech's brain is integrated to the ship computer.
The lonely astromech really would like to be rebuilt and go home to his master. (Check was PPPBB)