How can I make a trapezoid for Gradient Echo(for Magnetic Resonance Imaging gui) ?

Hello, I'm trying to build a gui for MRI. I need to build a trapezoid to create a gradient echo. I don't want to use the default function of Matlab for a trapezoid because i want to have at least 3 parameters such as ramp1 and ramp2 for the left and right sides and a constant value for the amplitude. If anyone could help me with this I would appreciate it :)

Thank you!

[José-Luis]

What have you done so far? What problems have you found in your implementation?