I Asked an AI Agent to Design a House for a Patch of Desert. It Drew Three Budgets in One Night.

A developer tasked an AI agent named "land purchase" with designing an off-grid earthship on a 1.25-acre Mojave Desert lot, and over a single overnight session the agent produced five site plans, three budgets, two floor plans, a cross-section and a true-scale 3D model. The agent pulled county GIS parcel lines, USGS 3DEP topography, OpenStreetMap roads and Desert RL zoning rules, then used the county's 20% lot-coverage cap to drive the design, landing at 10,776 sq ft (19.8%) with 109 sq ft to spare. Its bottom-up DIY budgets ranged from $88.6k to $251k, and it flagged that rainwater catchment of roughly 19,700 gallons a year would not satisfy the county's approved-water-source requirement, leaving a well or district hookup outside every budget.

Previously: I gave an AI agent one job: find free money https://blakelapierre.substack.com/p/i-gave-an-ai-agent-one-job-find-free , where 279 of 314 hourly scans came back “QUIET.” This one is a bonus. It isn’t about making money. It’s about spending it, carefully. I’m looking at a 1.25-acre lot in the Mojave Desert. The asking price is $4,000. I’ve emailed the seller’s agent about a possible offer at $3,000, and nothing is agreed yet. If it happens, I want to build an earthship on it: a mostly off-grid house made of rammed tires and earth, bermed into the ground, with a wall of sloped glass facing south. So I spun up a new agent, named it “land purchase,” and started asking it questions. Between about 10:30 PM and 5:45 AM, it produced five versions of a site plan, three versions of a budget, two floor plans, a cross-section, and a true-scale 3D model. Every number below came out of that session, and every one of them is an estimate, not a quote. The agent was strict about saying so. Step 1: Look at the dirt Before drawing anything, it pulled real data: - Parcel lines from the county’s GIS. - Topography from USGS 3DEP elevation data, at about 1 m resolution, turned into 1 ft and 5 ft contours. The land slopes about 3% down to the north-northwest. - Roads from OpenStreetMap. The access road is unpaved. - Zoning rules: the county’s Desert RL setbacks 25 ft front, 15 ft sides and rear and a 20% lot coverage cap . On a 54,426 sq ft lot, that’s 10,885 sq ft of roof and hardscape, total. That coverage cap ended up driving almost every design decision. Step 2: Fit everything under 20% My wish list kept growing: a 3-bedroom house, a garden, 14 fruit trees, a greenhouse, a hoop tunnel, a pool, a steel shop building, an RV pad to live in while I build. Each time, the agent re-ran the coverage math. The final version lands at 10,776 sq ft, or 19.8% of the lot. That’s 109 sq ft to spare. To get there it: - grew the house from 90x25 ft to 130x30 ft 3,900 sq ft, 3 bedrooms , - shrank the rain-catchment liner from 6,156 to 4,608 sq ft, - buried all the water storage, which frees about 380 sq ft of coverage it flagged that the county still has to confirm buried tanks don’t count . Step 3: Water is the whole game The site gets about 4 inches of rain a year. The agent’s math: about 9,870 sq ft of catchment house roof, liner apron, shop, greenhouse, tunnel times 4 inches times a 0.8 runoff factor is about 19,700 gallons a year, or 54 gallons a day. Storage is 23,000 gallons, a little over a year’s worth, because desert rain shows up in a few big storms and some years it doesn’t show up at all. Then it told me the part I didn’t want to hear: rain isn’t enough for the permit. The county requires an approved water source, either a well estimated $20k–45k for roughly 250–270 ft or a water district hookup. That cost sits outside every budget below. Step 4: Three budgets, each one argued with For scale, the agent started with sourced per-square-foot prices. A turnkey earthship from Earthship Biotecture runs $300–425/sq ft, which is about $1.17M–1.66M at 3,900 sq ft. Scaled DIY ranges came out to roughly $130k–390k. Then it built a bottom-up DIY budget, line by line, with every line labeled as either its own estimate or a sourced price: - v1: $105k–251k. Buried manufactured tanks, licensed septic. - v2: $88.6k–205.7k. DIY lined cistern pits, composting toilets. - v3: $95.6k–223.1k. My own solar prices, my dad doing earthwork, earthbag walls, geothermal. v3 is the interesting one, because it went up even though two things got cheaper: - My prices for power: used panels at $0.19/W and LiFePO4 batteries at $110/kWh. That made a bigger 9.8 kW array cheaper than the old 7.4 kW one. - My dad has the equipment and will dig. $5k–12k of skid-steer rental turned into a $1k–3k fuel allowance. But I also asked for earthbag walls instead of free tires +$7k–16k, mostly cement stabilizer and plaster and a geothermal heat pump +$6k–12.7k . The agent’s recommendation was a hybrid: tires for the bermed retaining walls, earthbags for the interior walls, which brings the total to about $90k–213k . The part I’ll actually reuse The most valuable output wasn’t a number. It was the list of things I can’t DIY my way around: - A state-licensed structural engineer has to stamp it. Tire and earthbag walls go through the code’s “alternative materials” route, case by case. - If the county requires septic, a licensed contractor has to install it. No DIY. - Salvaged glass in the sloped wall has to be marked tempered or laminated. Old patio doors work. Ordinary windows don’t. - Ordinary above-ground poly tanks collapse if you bury them. - Trenches deeper than 5 ft need shoring. Call 811 before digging. What I learned about using an agent for this - One night, one agent, a real design loop. I’d ask “what if the house were bigger” or “what if my dad digs,” and it would redraw the plan, redo the coverage math, and re-run the budget. Each version is saved, so I can see what changed and why. - Labels matter more than numbers. Every budget line says E its own estimate , S sourced, with a link , or U a price I gave it . That’s the same rule from my bonus scout: mark what you couldn’t verify. None of this is built. The land isn’t even mine yet. It’s a very detailed conversation with myself, with an agent keeping score. — Blake Previously: I gave an AI agent one job: find free money https://blakelapierre.substack.com/p/i-gave-an-ai-agent-one-job-find-free , where 279 of 314 hourly scans came back “QUIET.”