Buying usually wins on day one and building usually wins in the long run — the question is when they cross. Add up each path's one-time and ongoing cost, and this finds the point where the cheaper choice flips, so you can weigh it against how long you'll actually keep the thing.
Costs
Build it:€up front, then€per month.
Buy it:€up front, then€per month.
Compare over the horizonThe horizon: how long you expect to keep using the thing. Costs are only totalled up to here, so it decides which side wins. ofmonths.
Cost over time
BuildBuy
€50k€100k€150k
now10 mo20 mo30 mocross · 13 mo36 months
13 moBreak-evenThe moment the two running totals meet — after which the side that was pricier up front becomes the cheaper one.
€86kBuild · 36 mo
€180kBuy · 36 mo
Build itBuying is cheaper at first, then building pulls ahead at 13 months. By 36 months you'd spend €86k to build versus €180k to buy — building saves €94k.