Idea is good to create a lib to read, modify or save DICOM file.
For that you should surely be through with the DICOM file format.
Even with dcmtk it will take a good amount of time to create application to read, modify and save DICOM file( which may even include DICOMDIR,.dcm etc).
I think it take a time span of 6 or more month to create a new library similar to DCMTK.
I hope a programmer should try for resuability. :)