I agree with my predecessors. To now start concrete planning, designing floor plans, contacting companies, etc., it is too early. However, I would still recommend keeping your eyes open, seeing what you like, possibly visiting one or two model home parks to see which type of house appeals to you, informing yourself about basic things (construction method, wall structure, different types of heating, rough price tendencies), reading forums, and such things. Possibly already roughly setting a budget and seeing what you can get for it, whether the budget can be reconciled with the desired house, taking stock of your finances and seeing which installment is manageable, roughly thinking about how the loan could be serviced if, for example, children arrive (if there are none yet). And of course: saving equity.
We did exactly that. Since 2014, the plan was to want to build in a few years. The plot of land was already bought back then. And since then we have informed ourselves and looked and so on and have saved a considerable amount of equity quite purposefully. We then started concrete planning in the summer of 2016. Construction then began in March of this year. The advantage of the long "pre-planning period" was that at the start of concrete planning in summer 2016, we had already decided many things, e.g. house type, house style, house size, type of heating, ventilation system yes/no, room arrangement/space requirements, etc... We also already had a rough floor plan in mind that we liked (and which ultimately – with slightly adjusted dimensions – it became). Thus, the actual planning went relatively quickly; from the first meeting with the architect to the submission of the building application only 3 months passed.