Can I make a raised flowerbed against my siding?
You can rot your siding wall, or you can change your plan.
With vinyl siding, IT probably won't rot, but the sheathing &amp; framing behind it surely will.
You either need airspace (not a plastic sheet and dirt) between the bed and your siding, or you need to replace your sheathing &amp; framing with something that won't rot. Building a flowerbed with two sides, one of which is NOT touching the house wall and has enough gap for ventilation, drainage, and debris removal is far more likely to succeed.
Other options (assuming you have normal non-rotting foundation above ground level and below the siding) would be to push (dig) the flowerbed down below the siding level, or else relocate it entirely and hang some flower boxes off the house if you want flowers there.
If you really want the bed raised and against the house, you can raise the foundation or lower the yard (the latter would probably cost less.)