so im making a house and i wanted some ideas of where to put it, i plan to have a forge outside aswell, i want it it to be away from cites and towns have a river and if i can close to the middle of the map

There are nice spots along the lake north of Falkreath. Also along the river leading towards the Solitude area.

the thing is i can not find any flat spots that i like, kinda forestry and i dont know hoe to change the landscabe

Due west of Whiterun is pretty flat already, but that might fail your cities/towns test. If you're more flexible about your location there's some vast areas of empty land near Winterhold, between Dawnstar or just north of Windhelm.