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Introduction
Hi, and welcome back to the Intermediate Artifacts session. We've built a dashboard and a quiz. Now it's time for mini apps that help you sell directly. In this episode we build a cost-of-goods calculator and an order form that calculates shipping automatically, then writes an order summary for WhatsApp.
Step 1: Write the pricing rules clearly
The first step is writing the pricing rules. A calculator is only as good as the rules we give it. Sunset Coffee's first rule is the price list for its four products. Second, in-town shipping is ten thousand rupiah, and free for orders above two hundred thousand. Third, opening hours run from eight in the morning to nine at night. Orders outside those hours are processed the next morning. Fourth, the delivery area is within the city of Bandung only. At a glance these rules look clear. But one word will cause trouble later: above two hundred thousand. We'll find it when we test in step four. Let's compare vague rules with clear ones. Cheap shipping is vague. Ten thousand rupiah within the city is clear and can be calculated. Free shipping if you buy a lot is vague too. What's clear is the exact threshold. Note that this right-hand column was written after the testing we'll do later, when Laras decides on the threshold. Morning to night gets replaced with exact hours, along with what happens when an order comes in outside those hours. Around Bandung gets replaced with within the city of Bandung only. Claude can't guess the area boundaries that exist only in your head. So before asking for a calculator or a form, write your rules like the right-hand column. This also helps the team, because Dimas and the customers read the same rules.
Step 2: A cost-of-goods and margin calculator
Step two is the cost-of-goods calculator. Cost of goods is the total cost of making one product: ingredients, packaging, and a share of fixed costs like electricity and rent. Laras asks for a calculator for the iced coffee cup. The calculator appears in the right panel. Ingredients eight thousand five hundred, packaging one thousand five hundred, fixed cost two thousand, so the cost of goods is twelve thousand rupiah. With a selling price of eighteen thousand, the profit is six thousand per cup, a thirty-three percent margin. Then milk prices go up. Laras asks: if ingredients now cost eleven thousand five hundred, is the selling price still safe? The numbers change instantly. The cost of goods becomes fifteen thousand, profit drops to three thousand, and the margin falls to seventeen percent. Now Laras has a clear basis for deciding: raise the price, switch milk suppliers, or cut other costs. To keep the math honest, watch four things. First, use ingredient prices from your latest receipts, not from memory. Second, include all the packaging, down to straws and plastic bags. These small costs are often forgotten. Third, spread monthly fixed costs, such as rent and electricity, over the number of cups you expect to sell each month. Ask Claude to explain how if you're not sure. Fourth, recalculate whenever ingredient prices change. You can reuse this calculator at any time; just change the numbers.
Step 3: An order form with automatic shipping
Step three is the order form. Laras asks for a form using the selling rules. Customers just pick a quantity for each product, and all the math happens automatically. The form appears. The example in the panel: one liter of iced coffee, one cold brew, and two iced coffee cups. The subtotal is one hundred seventy-six thousand, below the free shipping threshold, so ten thousand is added. The total is one hundred eighty-six thousand rupiah. Notice that this form doesn't ask for a name, address, or phone number. Customers still send that on WhatsApp as usual, so the form doesn't need to store any personal data. With this form, customers can work out the total themselves before ordering, and Dimas no longer has to recalculate on his phone's calculator. A good order form has four features. First, the quantity for each product is set with plus and minus buttons, so customers can't make typos. Second, the price breakdown is visible: subtotal, shipping, and total are shown separately, so customers understand where the final number comes from. Third, there's a warning message if the order is outside opening hours or outside the delivery area. Fourth, no personal data. The less data you ask for, the smaller the risk.
Step 4: Test with edge cases
Step four is testing with edge cases, which are situations at the boundary of a rule. Case one: an order of two hundred twenty-five thousand. We expect free shipping, and the result is right. Case two: an order of exactly two hundred thousand. This is where the word above causes trouble. Does exactly two hundred thousand already get free shipping? It turns out Laras never decided, while the form treats it as free. Case three: all quantities are zero. The summary button is disabled, as expected. Case four: an order at nine thirty at night. A warning should appear saying the order will be processed tomorrow, but no warning shows up. Out of four cases, two have problems. Without testing like this, problems only surface when customers complain. Laras decides the rule herself: free shipping starts at two hundred thousand, so exactly two hundred thousand is already free. She also asks for a warning outside opening hours. Claude fixes both in version two, and adds a useful suggestion: update the written rules on Instagram too, so the information on social media matches the form exactly. Notice how the roles are divided. Claude finds and fixes things, but the business rules are decided by the business owner. After the fix, Laras tests all four cases again.
Step 5: An order summary for WhatsApp
The last step is the WhatsApp summary. Laras asks for a button that builds tidy order text, ready to copy. The result appears in the right panel. Two liters of iced coffee, one cold brew, a subtotal of two hundred twenty-five thousand, free shipping, and a total to pay of two hundred twenty-five thousand rupiah. Below it is a note to include the address. Customers just press the copy summary button, then paste it into Sunset Coffee's WhatsApp chat. On the shop's side, Dimas receives the order summary from the form. The format is always the same, so it's easy to read. Dimas checks the total, then asks for the full address. The customer's math and the shop's math now always match, so there are no more misunderstandings about shipping. The customer sends the address right in the chat. Personal data stays in the WhatsApp conversation, not inside the form. These two mini apps, the cost-of-goods calculator and the order form, can be adapted for any business: catering, laundry, even print shops. Just swap in your price list and rules. Let's sum up. First, write your pricing rules clearly, with no vague words. Second, calculate the cost of goods and the margin, and redo it whenever ingredient prices change. Third, build an order form with automatic totals and shipping. Fourth, test the edge cases, and decide for yourself any rules that turn out to be ambiguous. Fifth, build a summary that's ready to send on WhatsApp. Dimas still reads every order before processing it, because the final responsibility is ours.
Done!
We've built a cost-of-goods calculator and an order form: writing the rules clearly, calculating the margin, working out shipping automatically, testing edge cases, and building a summary for WhatsApp. In the next episode we map out how our own business works: flowcharts and process maps, so everyone on the team understands the order of the work. See you there!
Practice exercises
Try these on your own after watching to lock in what you learned.
Calculate the cost of goods for one of your products with a calculator built by Claude
Build an order form with your own business's shipping rules
Test five edge cases and fix any rules that turn out to be ambiguous
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Cerdas Inovasi Digital Team
Software developers, BIM & 3D engineers, and AI practitioners
53 video classes1,290 episodes
We build software, BIM models, games and AI automations for clients every day, and turn that hands-on work into step-by-step classes: every step is shown on screen and comes with a PDF guide you can keep.
