playhouse bed ideas/suggestions?

Looking to build a playhouse bed for my 3yr old. I just started getting into woodworking within the past year so my knowledge base is somewhat limited as far as how to do it the right way. Have ideas of my own but looking to get some feedback from others. Would like to build as cheaply as possible so I'm thinking about making the frame out of 2x4's and 6's. Then doing the exterior/interior finishing with 3/4 MDF. There are some online that are quite detailed and I intend to use one of them as a model. All advise is welcome and appreciated.
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