Struggling with cost estimation part in some case questions

Hello everyone, I hope you all are doing good in your preparation. I am practicing case interviews seriously from last weeks, and I notice one thing again and again: whenever the case moves to the cost estimation area, I feel stuck. Market sizing, profitability tree, customer segmentation all these feel normal to me. But when interviewer asks me to break down costs, I suddenly lose confidence and I am not sure if my approach is right. Sometimes I try to categorize fixed and variable cost, sometimes I try to list components like raw materials, labor, logistics, overhead, but still I feel I don’t know how much detail they really expect. If I go too deep, I worry I am wasting time. But if I stay too general, I feel maybe I am missing points. In many sample answers, candidates make very neat structures and assumptions quickly, but for me it takes time to think. One example: recently I tried a production case where I had to estimate cost for a new manufacturing line. It remind me a bit of real technical work like structural steel cost estimation where you break everything into materials, weights, labor hours, fabrication, installation, etc. But in consulting case interviews we don’t get real numbers, so I can’t rely on exact data. Instead I must make assumptions fast, and sometimes those assumptions feel random to me. I really want to know how much detail is “normal” in a real interview. Do interviewers want us to list every small cost element, or only main drivers? Also how do you stay structured when you don’t know the industry? For example, in food industry case I have no idea about ingredients cost; in manufacturing case I don’t know machine operating cost; still I must say something logical. If anyone here improved in this part, please share your method. Do you use any framework or simple checklist for cost estimation? Something like always checking materials, machinery, labor, distribution, overhead, etc.? Or do you think from value chain perspective? I will appreciate any guidance because this part is becoming my weak area, and I want to fix it before real interviews.