Not really sure what method you are using to make your Macaroons but i will try to suggest a few things that could be the cause of your hollow macaroons.
Make sure that your meringue is really very firm. If using french meringue, whip until very stiff peaks, if a little afraid of overwhiping add some cream of tartar 1/8 tsp per egg white or lemon juice to the meringue. Also feel free to add the suagar right at the start of whisking the egg whites, it won’t affect the final product. If using the Italian meringue method, make sure that you allow the egg whites to become cool once you’ve added the syrup. The side of the bowl should feel only very slightly warm to touch. Also don’t allow the whites to get too stiff before adding the syrup. Add the syrup at the soft peak stage or just before.
When mixing all your ingredients together, don’t be too cautious. Feel free to mix as hard as you like. You want to knock out the air, there is enough water in the mix to make the Macaroons rise. A good rule is to mix until the mix easily falls from the spatula in almost continuous form, or it you drop a little of the mixture on top of itself it should almost sink back into itself after 10 seconds. It is definitely a stirring/beating motion you want to employ rather than a folding one.
It could also simply be that your oven is too high, 135C (convection) is ideal for a 3 -4 cm diameter macaroon that takes about 15 - 17minutes to cook.
I hope one of these suggestions helps, if not feel free to post the recipe and any other information you think might be useful and I will try to help some more.
Best of luck, and let us know how you get on.