Craft DC to build a room or building

[Echoen]

Using the alternative crafting rules (http://www.d20pfsrd.com/skills/alternate-crafting-rules/) and knowing our craft (carpentry) check result, all that's left is to determine whether a given room or building (from the Downtime rules) is Simple, Normal, Complex, or Intricate.

However, there's no criteria set forth to identify the DC for a room or building.

Example:

Crafter has a check result of 45, with 10 unskilled laborers aiding.
An animal pen costs 250g.

Normal: DC beaten by 30 = x6 base progress = 12g progress per day.
Complex: DC beaten by 25 = x5 base progress = 20g progress per day
Intricate: DC beaten by 20 = x4 base progress = 32g progress per day

Normal: 21 days to complete
Complex: 13 days to complete
Intricate: 8 days to complete

[Fuzzy-Wuzzy]

Actually you go a bit faster than that, since beating the DC by 0 still gets you x1 base progress. Your list should be

Normal: DC beaten by 30 = x7 base progress = 14 gp/day (18 days)
Complex: DC beaten by 25 = x6 base progress = 24 gp/day (11 days)
Intricate: DC beaten by 20 = x5 base progress = 40 gp/day (7 days)

An animal pen is probably Extremely Simple, so DC+40 => x9 progress => 4.5 gp/day => 56 days(!). OTOH it's listed as taking 16 days to have built. Working backwards, 16 days => ~16 gp/day => x32 progress for Extremely Simple => DC+155 = 160 check result => highly implausible.

*scratches head*