Hi,
We ordered bathroom ceramics and vanity units from Hornbach. They have a lowest price guarantee that they really stick to. In other words, they match _ANY_ price and even undercut by 10%. This explicitly includes online shops. It worked very well for us! However, they are currently cutting down their range; until last year, they even ordered items for you that they normally don’t stock. Now you are limited to the "normal" suppliers. Keramag is included there as well.
Personally, I would always buy the kitchen (only the furniture) at Ikea and have the assembly done via Blauarbeit.de or MyHammer.de. Appliances then from an online shop. Of course, you have to be able to plan that yourself.
We bought parquet flooring from a local timber dealer, who lowered the price from about €55/sqm to about €35/sqm after several rounds of negotiation.
For the outdoor facilities, you can save some money if you let the shell constructor do the roughest work. They normally use really large equipment, where 250 sqm of topsoil can be leveled quickly or 50 sqm of driveway can be gravelled fast. The garden landscapers often come with these mini excavators, which per hour aren’t much cheaper (the driver is the expensive part!), but move only 1/10 of the quantity of a large excavator in 5 hours.
Regards,
Andreas