Your question is very unclear because you have not used punctuation or capital letters. My guess is that it is a conversation which should go like this: 'I don't think installing an open plan office was such a good idea .' 'Me neither. It was indeed a bad idea.' So your answer is 'neither'. If the first person says something negative, you agree with them by saying 'Me neither'. You would say 'Me too' if the first person said something positive. But please remember to use capital letters and correct punctuation. These things are not optional - people may not understand what you are writing if you don't use them.

If I understand your question right, the way you would write it is "I think installing an open plan office was a bad idea as well" using the two phrases your provided. Neither could be used in this way within this context: "I think installing an open plan office was neither a good idea or a bad one." Hope this helps :)