Custom Vehicles?

[Strigon]

Are there any rules out there for constructing a vehicle that isn't listed in any rulebooks? Or would the DM simply have to find the cost of materials, cost of manpower, and how long it would take?

For example, in my current (high-level) game, some of my players want:

- A gnome submarine, but on a much larger scale.
- A giant dirigible (almost a flying fortress).
- A tank, either technologically fueled (Gnomes) or animated.

Depending on the cost, I'm sure they wouldn't mind having an entire battalion of tanks, all loaded onto their dirigible.

How on earth would I go about finding the cost for these items?

[Alistaroc]

Larger submarine? Easiest way I can think of is to make each increase in size category multiply the cost by 2.

Also, the Sailing Ship is an above-water Submersible for 10k, compared to the submersible's 80k. So find a larger ship in Stormwrack or the A&EG, maybe a longship, greatship, or galley, and add 70k to its price to make a larger submersible.

A bigger dirigible? Is a Zepppelin not big enough? If you need bigger than that, you can outfit any ship, such as a greatship, with the Cloud Keel(A&EG49), or failing that, the Stronghold Builder's Guidebook includes costs for creating a flying stronghold. And that can be pretty much as big as you want.

A tank?
Halfling War Wagon with a ballista on it, install a lightning turbine for 90k, and a continuous item of any electrical spell. Should run you about ~100k.

[noob]

Craft a at will command word guards and wards (costs 118800 po) and use the windy corridors with turbines to produce energy in each of your tanks.
You can place dozen of turbines in one corridor and so have a good energy production and so now for a simple action you make a tank powered for 22 hours(and also you do not need to know electrics and so you only need some knowledge on windmills and a not so costly item and you can power thousand of tanks with this item(in one hour you make 600 tanks powered for nearly one day))

[Strigon]

I suppose those all make sense; and as for whether or not a zeppelin is big enough?
Apparently not for my players. Which makes me wonder what they're planning (or what they think I'm planning...)

[Uncle Pine]

Stronghold Builder's Guide has rules for creating burrowing, crawling, flying, plane-shifting, sailing and submerging strongholds. A "stronghold" can be as small as 20 ft. x 20 ft. x 10 ft., so you can easily make vehicles.

[Strigon]

Stronghold Builder's Guide has rules for creating burrowing, crawling, flying, plane-shifting, sailing and submerging strongholds. A "stronghold" can be as small as 20 ft. x 20 ft. x 10 ft., so you can easily make vehicles.

Aye; ironically, I had considered asking them to put together a stronghold, and then use Wondrous Items to make it all work. Didn't think to check whether or not they actually had rules for such structures!

[noob]

Strongholds are going to be more costly(by a factor increasing with the number of tanks above 10 (It is for the cheapest stronghold tank 6000 PO(stone or iron walls) + 5000 PO for movement at the slowest speed possible)) than making mundane tanks with corridors filled of helices and using the magical item I suggested but the interest is that the GM is more likely to allow strongholds rather than allowing the most cheated and funny tool ever(there is even the suggestion zone for making people your slaves for having the driver for free two casts and you have a driven tank).