How to build a massive single-family house most cheaply?

That's right.
We built a very affordable 256m2 two-family house with a double garage of 56m2 in solid construction during Corona.

Here are my tips on how we built with high quality for about 1800€/m2.
0. Put together your A team one year before construction begins. You have to find the right workers, at least two for each trade. That way you have backups in case someone drops out.

1. Build with a local construction company with a good reputation, no prefabricated houses. You want to use the plot optimally and for that, you have to study the building regulations and get the maximum out of it with architects. Hire a separate planner for heating and water and pass the plans on to the construction company. Floor plan planning is something you can learn cheaply and then you just have to decide what fits the family. Botched building services cost thousands of euros extra annually for heating because, for example, pipes are too thin and the heat pump constantly cycles on and off or you get sold lots of unnecessary mixers.

2. Have local companies do earthworks, foundation slab, masonry, roof, tinsmith, and windows. For the roof, you can arrange to prime and paint the rafters yourself. For drainage, you can buy the pipes yourself and prepare pipes and house connections with an excavator operator.

3. As soon as the roof is up, you should start building the attic immediately. Applies to a gable roof. Building the attic yourself by laying plank paneling is simple and significantly more valuable than OSB or other glued materials that off-gas. When the attic is done, you can also install a photovoltaic system yourself, and you should arrange this directly with the electrician and submit applications before starting and ordering materials. Our 10kw photovoltaic system cost about 7000€. Then laying insulation between the rafters yourself is perhaps the nastiest job, but you save a lot. I installed 320m2 of rock wool and another 80m2 of Knauf insulation under the rafters. I ordered the rock wool cheaply on pallets at the OBI building materials hall and stored it in the garage. The vapor barrier foil Intello Plus as well as sealing tapes I ordered at Baunativ.

4. You can also get electricians and plumbers to work if you want. I ordered all plumbing materials myself according to the planner's list at a specialist dealer and had it installed according to plan. I ordered my heat pump from RJTec and commissioned/programmed it myself.

5. You can also prepare screed work yourself, such as taping bitumen sheets and insulation. The screed layer provides the material. Also make sure to use PIR against the soil and insulation with better impact sound reduction on the upper floor.

6. For plastering work, the be-all and end-all is to find a cheap local building materials dealer who orders the silo for you as well as all materials like bonding bridge, mesh, plaster rails, APU trims, topcoat plaster, and paint. That saves a lot.

7. The same applies to tiles. But tiling should be done by a professional, it’s way too time-consuming for beginners; you can at most assist by pre-coating the tiles.

8. Kitchen: Hire an independent planner and order the cabinets and possibly appliances through them. Assemble yourself.

9. Outdoor area. Take your time for planning here and consider what you want to do yourself and what not.

Bonus tip: live next to the construction site and have an apartment with a basement to store materials and tools. House first, then children. With small children you cannot do any DIY work because you won’t have the time.

I bought a house from the 1950s and now want to do a relatively extensive gut renovation (budget 750k). Could use someone like you