can anyone give me advice, an online reference or tips on scratch building tanks, aircraft etc.

I'm currently trying to scratch build a helicopter and i found it very frustrating to work on it. not to mention it's very challenging for me.

Thank you in advance

A chopper sounds like a complicated first project to me. Have you considered starting with a simpler shape on which you can practice the basics of measuring, marking out, cutting, fitting and assembling? The first things I scratchbuilt were boxy shapes (literally boxes), which I then followed with a Beaverette armoured car (all flat plates except the drum turret). I've never seen a simple helicopter and aircraft by and large have lots of compound curves which are hard to measure and build accurately. I'd want loads of reliable drawings and cross sections too and having just examined the Soviet Mil 24, I can confidently say that I won't be even thinking about scratchbuilding one of those as the whole fuselage is twisted from front to rear to counteract aerodynamic problems.

There is an specific book announced to be published soon:
http://armorama.com/news/21429

I be it will be more than helpful, however I have to agree with Robert: you better start with something simple and gradually increase the complexity.

Another option to consider nowadays is to create the model using 3D software and then get it printed.

I have started smaller scratch built items and additions on models before such as putting a mounted gun on an MI-17 or putting all sorts of mods kits, but i never attempted to fully make a kit from scratch.

The reason why i wanted to scratch build a helicopter is because the original one had a lot of mistakes and i thought it might be better if i build one from scratch.

If a full scratch build will be too difficult for me than i'll just try and do scratch building on a base model instead.