It might sound a fun idea but I strongly suspect you are going to ruin what looks like a nice playhouse and end up with a very poor hen house. Sorry to sound negative but why not sell the playhouse, which looks in reasonable condition, save yourself a lot of work and buy a purpose built hen house. Poultry houses have a lot of design features born out of years of experience and if you don't know about chx needs you are going to make a lot of mistakes trying to convert what in all likelihood is an inappropriate building. Beginners always think a hen house is just a shed with chx which is far from true.
A few problems spring to mind just looking at it. It's much too big for starters unless you want to keep around 50 hens. A 1 metre square house will easily house around 12 hybrids. Chx only need a house for roosting in at night and laying in if that's where the nestboxes are, though they can be separate if you wish. A hen house needs to be snug and dark, weather proof and secure which means fox proof boarded, raised off the ground for warmth and to discourage rodents, lots of access for cleaning. It needs to have baffled ventilation not draughty windows which let in light and wind. It needs to be completely weatherproof with tongue and groove boarding or high grade sheet material. Roof felt is a big no no as it harbours red mite, corrigated bitumen impregnated board such as Onduline is best. Nestboxes ideally should be external.
If you want to see what a simple to make but good design looks like see diggits post on a coop he is building from sheet material. This has lots of practical design features which will help discourage red mite and be easy to maintain and be chicken friendly. However I suggest the starting point is to learn about chicken keeping and methods of husbandry first before you think about housing. Actually the base material is fine but run area you will need is at least 2sq m per bird and actually a well designed run is every bit as important as the house. Chicken wire is not fox proof as it untwists if chewed or stressed too much, 19swg weld mesh is.
Best of luck whatever you do.