I was just wondering, if a player wants to build a custom weapon (ie bowcaster) How would you guys go about doing it? Obviously some sort of mechanics check, cost for parts, and down time. But what would you set the difficulty at? what would you do with Advantage, threat, Triumph, or extra successes?

This depends. Do you want your character to be able to fail? If not, I would just charge the same amount for purchasing the weapon, and have the character build it during down time. With Wookiee bowcasters in particular, it's something of a cultural touchstone to build one's own weapon. If that's what you're going for, you could just let it happen.

Weapon attachments work this way: pay the credits, get the thing, even though it is a modification/personalization of the weapon or armor in question. If the character wants to improve on it, that's when the Mechanics checks come into play. I would run a home-made weapon the same way.

I agree with JRRP. No check necessary. If the player really wants to make a mechanics check, just have him "purchase" and modify an attachment to coincide with the construction of the thing.

I might go with no roll necessary, but have them roll anyway. One way or the other, you get the weapon together - but lots of advantage means that it's well crafted and looks nice, lots of success means that you can bang it out over a weekend. Lots of threat means that's kind of plain or frumpy looking and lots of failure means that it takes you two weeks and runs you and extra 50 bucks for replacement parts after you drill through the motherboard.

Agreed — use the success/failure dimension to control how quickly it is made and/or for how much, and use advantage/threat to control the quality of the resulting craftsmanship, etc….

The weapon will get made, period. But there are variables in how well and how quickly it gets made, and that’s what the roll is for.

In my AoR game when the Wookiee medic (don't ask) got enough credits to afford a bowcaster my handwave was he'd had to pay that money to get his bowcaster brought in past imperial customs. The shared logic of me and the player being he'd came to the planet on public transit and couldn't bring the weapon.

One thing I've been doing for my Outlaw Tech is allowing him to build nonrestricted gear equivalent to the value of the spare parts/forage/junk he's been able to scavenge. If he has tools and a workshop, I let him do it during downtime with no checks, unless he's attempting to modify the standard items. That said, there's certainly some potential for abuse here with the wrong player.

if he's good for cash, or he is willing to work for it, building his own could explain him having a bowcaster with the superior weapon customisation attachment. (6250cr total)

he pays the cash, makes an average mechanics roll, apply results as mentioned above.

You could also role-play getting the superior quality components using knowledge checks, streetwise checks, negotiation checks, even vigilance checks. all of these could have an effect on the overall quality of the weapon, and how long it takes to do.

I wouldn't reduce the total cost by more than 1000r or roughly 15%. but things like triumph could be interpreted as finding cheap or even free other attachments (Probably the Bowcaster Accelerator enhancement, 250cr, EotE p 189, due to it being more in line with he work being done)

First of all, Thanks for all the responses. My GM and I went over the responses, and he decided to make me roll against 3 purple based on the rarity 7. After that extra successes he allowed me to convert into HP attachments that I wanted to signify my character creating it to my personal specifications.