Biplanes just need that extra bit of care when building,once you have two sets of wings made up and the centre section strut arrangement is made then is the time to start thinking about how you are going to rig up the wings to ensure that a/ they are both set up at the correct angle and b/ that they are square and true to the rest of the airframe. Whether it be a simple plastic kit or a flying model the same principles apply and a similar set up can be used for both applications,for the task all you will need is some foamboard or similar material,this is how it is done- Firstly look at the side view on the plan and trace the upper wing position,then the lower wing position,al you need to do is to trace the aerofoil sectins in relation to each other and mark a known datum point of the fuselage,we are assuming that the centre section struts have been made up but if they have not well it does not matter really at this stage,they can easily be added later,the main object is to set up both wings with accuracy in relation to the fuselage. Next trace the wing positions onto two pieces of the foamboard and then cut out slots where the aerofoil positions go,assemble the lower wing to the fuselage and make sure this is the correct position and that it will not move in future,now slip the foamboard onto both tip of the lower wing followed by the upper wing,so we have before us a jig with both wings inserted but minus the wing struts. Next take some strip wood and carefull tack glue four pieces to both wings so that on the inboard section we have one strip which runs from the lower trailing edge to the top trailing edge,now do the same but at the wing tips so we have both wings locked firmly in place. The only thing that remains is for the wing interplane struts to be made up and attached with brackets or whatever your favourite system is,I use alloy brackets bonded to the ribs and bolted for security and then miniature split pins to hold the struts in place,there are dozens of different ways to go about this job bit the main thing is that you wings are firm and secure. All that now remains is to remove the foamboard jigs to leave a perfectly rigged set of wings,dismantle the lot and carry on with the construction of your model.