My table group wants to build a wall to protect a village from future invasions. They intend to cut down the trees around the village and use those as the primary material.
How long would it take a group of 5 people to build a wall of roughly 1600 feet [490 meters]? I'd like to have a starting point to calculate.
This question takes a lot of assumptions to answer properly. I'll give it a shot though.
(1) A wall can be approximated by two sideways ladders stacked on top of each other, lashed together with rope between 10-foot-poles.
Add up those costs and we get 1.25 gp / 10 ft, or 200 gp for 1600 feet.
Given the standard crafting rate of 5gp / day, a single person would, given all the raw materials, be able to craft this wall in 40 full workdays (40 feet per day).
5 people could finish it in 8 full workdays.
Personally, if these people are not trained carpenters, I would double that time.
But they don't start out with all the raw materials - they need to get those.
(2) Unfortunately, we don't have official stats for a tree - the closest I could find is a Treant - with AC16 + HP138.
A commoner proficient with a Handaxe would have a 35% chance to hit for 3.5 damage, which comes out to just about 11 minutes of constant chopping to fell one tree.
(3) Then we need rules for turning a tree into wall-sized chunks. Branches can use the small resilient wood object statistics (AC15, HP10) and would take a little over half a minute each. Around 20 branches adds another 10 minutes, bringing us up to a 21 minute total for one tree.
(4) A single solid trunk probably isn't very useful for wallbuilding, so cutting it again would be necessary: add on another 11-minute chopping session to cut it down to size.
(5) Observing the Treant picture in the Monster Manual looks like one tree could be used as the materials for 20 feet of wall - so we're looking at chopping down 80 trees for your full wall.
(6) A Short Rest between trees to regain strength brings us to ~1.5 hours per tree, or 5 trees per day. That's 16 days of 1 person collecting materials, or 4 days for 5 people (because you can't spend fractional downtime).
Using those 6 assumptions and adding all this together gives 12 days to create a wall from scratch if 5 commoners - proficient in carpentry - devote all of their time to doing so.
However, if you instead have two 9th level sorcerers, you can create a 1600 foot wall in 40 minutes simply by 4 casts each of Wall of Stone, making a permanent 200ft x 10ft x 3in wall each time.
5e has a little bit of guidance on this sort of thing. It's useful, but perhaps in the way one might initially think. From DMG p.128 we can see:
\begin{array}{lrr} \textbf{Stronghold} & \textbf{Construction} & \textbf{Construction Time} \\ & \textbf{Cost (gp)} & \textbf{(person-days)} \\ \text{Abbey} & 50,000 & 400 \\ \text{Guildhall, town or city} & 5,000 & 60 \\ \text{Keep or small castle} & 50,000 & 400 \\ \vdots & \vdots & \vdots \end{array}
So the first approach is to simply ballpark it: what from this table seems like it'd take the same effort to build as your town wall? Maybe "outpost or fort," clocking in at 15 Kgp + 100 days? Or a "trading post" at 5 Kgp + 60 days?
But the simple truth is that 5e doesn't natively support the sort of precision you seem to be looking for. So we've got two paths forward:
I've written elsewhere about how well 2e campaign and DM resources seem to play with 5e numbers, so I won't belabor it here. I'll point you to pp. 48-61 of 2e's The Castle Guide and point out that (assuming a PM of ~2/3, derived from moderate agriculture, near resources, a well-motivated workforce, rolling hills, &c.) and note that the construction of 160 10'W x 15'H wooden wall segments will run your party 32 weeks and 800 gp.
I guarantee that the designers of 5e were well-acquainted with the vast back-catalog of supplementary materials. The fact that they included only a small sample of building types and costs wasn't (just) to save space, it's also to encourage you to spend less time on these details. "Just pick something close from the table, call it an outer wall, and move on" is their explicit philosophy. (As much has been written in design commentary/articles which WotC cunningly hides on their website, more secure in that lair than any of Acererak's treasures.)
you don't have to be them. Do whichever works for you. You'll be in good company--why do you think I didn't have to look up those page numbers in The Castle Guide?
=)
