The other way around would mean that you do the work you put into the house just as quickly and well as the professional, which is rather rare. If you now take 50% longer, you can spend 150% of your hourly wage for the professional. That should fit well...
A rule of thumb for Germany is a factor of 1 to 5: So to commission 1 hour of your own work (gross price without material), as an employee you have to pay about 5 hours net.
The "remaining" 80% of the paid wage is shared between employers, the state, social security funds, landlords, lessors and the Chamber of Commerce.
Elsewhere in neighboring countries it is rather 1 to 3. Among other reasons, formalistically we may be a "rich country," but not as much of it reaches one as in other "rich countries." At least as an employee. For employers, the state, social security funds, landlords, lessors and the Chamber of Commerce it may look different :p:D