As long as the area around your downspout of your gutter doesn't stay soggy it should do ok...Clematis like their roots to stay moist BUT not standing in soggy soil..so you'll have to decide those conditions yourself..When mentioning roses ..we are talk about climbing roses..those are best as they can overwhelm a rose bush..I have mine on rose arbors with my climbing roses and Obelisk, Tuteurs, one is climbing my lemon tree..when planting with trees the roots can compete...so make sure that it is far enough away and where the soil moisture will be condusive with its needs...I have also attached wire fencing to my brick on my home and have them growing up that....And up my Pergola with my climbing roses and in pots with obelisks...Jeanne

Here is a link to my Photobucket album showing a variety of supports to grow clematis on. Your imagination is the only limiting factor in the number of items that can be used to support clematis.

Here is a link that might be useful: Garden Supports

I bought some 64" black wire obelisks at Lowe's and the clematis have taken to them with a grateful sigh (they were making do with tomato cages). These are to use as vertical accents in mixed beds which include shrub roses. Now I'm on the look out for a few taller obelisks for higher growth. I can't reach up very high but the obelisks are easy to install and the clematis have no problems getting a grip on them.
And I figure the wire designs will be acceptable in winter as well.

Some are on lattice trellises, some on nets stapled to cedar fences, some on arbors, some on lattice fences, some on obelisks, some I'm trying to get to grow through shrubs but they seem to prefer to ramble on the ground.