How to create Polygon features associated or parallel to given Line features

Example:-

So we need 2 feature layers,
1) Line feature layer (Layer Name – Lines) as input which has some random line or poly line features.
2) Polygon feature layer (Layer Name – Poly) as output which will be updated or inserted with polygon features based upon available line features in given input (Lines) feature layer.
Input parameters:-



This tool has been built in c#.net whose .tlb file is imported into Arc Map to perform the given actions.
The feature classes drop down lists or combo boxes are loaded with all the available feature layers in the given map or .mxd document.
I have placed my tool in GML name space, so you can find GML button in Arc map interface while importing this .tlb file.
Output:-



Before generating polygon

After generating polygon using my tool