One thing I’ve noticed is that the “quality” level of tools doesn’t mean much other than enabling a higher tier of things to be built. Also, all crafting and construction takes the same length of time regardless of how skilled or well-equipped the player is. What if the length of time it takes to craft something was derived from how capable someone is of crafting that type of item?
The solution is to quantify the amount of work that must be done in order to craft something. In reality, this is the number of stitches and cuts required to make the t-shirt, the number of cuts required to make a spear, or the number of cubic meters of dirt that must be displaced in order to dig a pit. Someone with higher skill at sewing should be able to make the same garment as strong with fewer stitches, or may be able to stitch more quickly. Someone with a better shovel should be able to excavate a trench more quickly.
I propose that all craftables and buildables have a metric called work points, that is related to the length of time that it takes to create with minimal skills and minimal tools. For example:
100 work points
skill: level 0 fabrication
tool: level 1 cutting quality
component: one heavy stick
Then, say that each level of fabrication reduces the amount of work points for all fabrication-based items by 10%, so
Level 1: 90%
Level 2: 81%
Level 3: 73%
Level 4: 66%
…and so on.
Similarly, say that different tools have different amounts of build-points per minute.
Makeshift Knife: 5 points/min
Pocket Knife: 6 points/min
Survival Knife: 10 points/min
Circular Saw (on): 50 points/min
…and so on.
For construction, everything would be very similar.
1000 work points
skill: level 0 construction
tool: level 1 digging quality
Each level of construction reduces the amount of workpoints by 10%.
Digging Stick: 10 points/min
Stone Shovel: 20 points/min
Shovel: 25 points/min
Entrenching tool: 35 points/min
Backhoe: 200 points/min
You could also have fun with stats. Maybe strength confers a bonus to construction rates and dexterity to manual tasks.