hi there! i hv  a cheap china made heli (not very powerful) , i wanted to use its motors n elecronics to make an micro plane, its 3.5 channel tx n rx , two mian rotor motors 1 tail rotor motor esc,reciver,,how should i make the stucture of plane n ? of what material,i hv thought of using tail motor as servo motors for    radar n two main motors on two side wings.

http://www.ebay.in/itm/RC-metal-helicopter-aeroplane-remote-toy-kids-gift-big-/251075613424?pt=IN_Toys&hash=item3a7545d2f0#ht_2422wt_1269

I can only tell you are on right tracks for making one such micro.

However such micro is good for flying indoors and outdoors only on a calm night due to drastic reduced range of IR  in daylight.

You may get some ideas from here

http://www.rcindia.org/electric-planes/indoor-micro-flying-under-20-gms-diy-projects/msg11338/#msg11338

thanks for link , but i was much uncertain  about what material should i use . and wat should be structure

This is another good attempt by vineet.

http://www.rcindia.org/electric-planes/the-'lisra'-micro-under-20-grams/msg87506/

Biofoam disposable plates and kebab skeevers are good materials to start with for structure.