making layers block, adding layers

hi, i'm trying to make (a) structure, and each U, D, R, S blocks are (b)~(d)

and i don't know how to build it, i mean should i make a function for each blocks ? if i have to, how should i set the element of function?

+ i was making (b) block and it's like

Downsampling = [

batchNormalizationLayer('Name','batchnorm_1')

reluLayer('Name','relu_1')

convolution2dLayer(3, 32, 'Stride', 2, 'Name','conv_1')

batchNormalizationLayer('Name','batchnorm_2')

reluLayer('Name','relu_2')

convolution2dLayer(3, 32, 'Stride', 1, 'Name','conv_2')

additionLayer(2,'Name','add')

];

lgraph = layerGraph(Downsampling);

skipConv = convolution2dLayer(3, 32,'Stride', 2,'Name','skipConv');

lgraph = connectLayers(lgraph,'skipConv','add');

i don't know where to put skipConv layer....