New model in the worldeditor

I have a problem:

I created a new model building and I want to put it in a map but i don't want to replace an other model,

so i created a new custom unit whit base model humanlumbermill
I changed the use model property to my new model : own_models\building01

but in the editor it uses the standard extension .mdl (witch i think should be mdx, but i cant change it) and it won't load my model, i added the model to war3patch.mpq as own_models\building01.mdx and own_models\building01.blp.

In game it doesn't work either

I tried to add it in the worldeditor 1.12 and WE Unlimited, but both use extension .mdl and both won't load my model.

what should i do, or what world editor should i use???

I'm not sure if it will solve your problem, but I had similar troubles importing a .mdx, and I just changed the extension of the actual file being imported to .mdl and it worked.
Dunno why emote_confused

Thanks for the suggestion Ligature but it doesn't work