Your layouts must be named the same as your .ini files. Unzip your zipped layouts in the custom folder one by one. And rename them if necessary. They can all be in the same folder since they'll be named differently. Here's an example of what it should look like: if you're ini is named
atari2600.ini = atari2600.lay, atari2600-main.jpg, atari2600-message
mame.ini = mame.lay, mame.ini =mame-main, mame-message
Open mamewah.ini and make sure it's like this
### Misc Options ###
layout custom