All the maps that I made that have a painters name on it were done freestyle.
I just decided to do a map and made it up as I went along...Can you tell?
I don't recommend this technique at all, never, ever, ever.
Draw it out.
Once you get proficient at the mapping tools you can actually draw it out in the tool.
I have a pile of maps that will never see play cause they just never ammunted to anything...Now that I think of it, maybe I should have left a good number of released maps in that state.
Plan, think, plan, think some more, build, think, get input, think, rebuild, think...etc... till it's a work of art!