For some reason many if not most guides and tutorials emphasize leveling in conjunction with base building. They're generally full of crap... unless of course you are not playing in survival mode - in which case use creative mode and mods - play Viking architect to your heart's content.

In the Valheim survival reality.. you really don't need to level all that much. Learn to use struts for foundation supports and just raise/level specific small areas for particular needs - like for campfire/hearth or kiln/smelter - things that require being on the ground (or on stone or certain trees as an alternative).

If you really must have a level area for some reason - like perhaps you don't like farming on a hillside, there are naturally occurring reasonably sized already mostly flat areas to be found in Meadows.. the stone circle (aka alternate unused spawn sites).